7. Fotooxidacion en Helados de Crema

I

ISensory and Nutritive Qualities of Food

JFS: Sensory and Nutritive Qualities of Food

Photooxidative Stability of Ice CreamPrepared from Milk FatM. SHIOTA, N. IKEDA, H. KONISHI, AND T. YOSHIOKA

ABSTRACT: The photooxidation of ice cream containing 14.25% milk fat prepared from 7 fat materials with different compositions was investigated by conducting sensory evaluations for oxidized off-flavor and by monitoring hydroperoxide formation. They showed a wide range of oxidative stability against light, and the flavor score was related to peroxide value (correlation coefficient, 0.795). The photooxidative stability of ice cream was influenced mainly by the riboflavin content and by the oil’s susceptibility to photooxidation. These contributing proportions were 53.7 and 17.6%, respectively, with a multiple regression model. The photooxidative stability of the oil fraction increased with the increasing tocopherol homologues ratio, g-tocopherol/a-tocopherol (correlation coefficient,0.846). Furthermore, the photooxidative stability of ice cream was influenced by the amount of free-fat content.

Keywords: ice cream, milk fat, b-carotene, tocopherol, photooxidative stability, riboflavin, transition metal, free fat

IntroductionCE CREAM IS A FROZEN DAIRY PRODUCT THAT IS WIDELY CONSUMED

throughout the world. It contains approximately 8 to 15% fat (Li and others 1997) because fat plays an important role in bring- ing the desired characteristics to ice cream: a smooth, creamy,

soft feeling in the mouth, and a good flavor (Guinard and others

1997). Ice cream has some unique characteristics such as the sol-id fat network ( Thomas 1981), and these characteristics have been studied by many researchers. Schmidt and Smith (1989) reported the effects of processing condition on the physical properties of ice cream. Goff and others (1989) studied the influence of milk components on the physical properties of ice cream. Ohmes and others (1998) reported sensory and physical properties of ice creams containing milk fat or fat replacers. Most of the research on ice cream has focused on its physical characteristics and sensory aspects.

Recently, most grocery stores have adopted stronger lighting than ever on food products to show their products attractively. Since the business hours in grocery stores are often extended, the potential risk of light-induced degradation of food products would be increased. Deterioration resulting from oxidation during storage has not been considered an important problem for ice cream because ice cream is usually kept in frozen conditions at –18 to –20 C (Azzara and Campbell 1992). Ice cream, however, contains a high percentage of fat compared with other food products; therefore, ice cream might deteriorate during storage under strong lighting in grocery stores. Light-induced oxidation could potentially cause serious problems in the quality and safety of ice cream.

With respect to light-induced oxidation of edible fats and oils, several articles have been published. The oxidation strongly depends on the fatty acid composition of oil in the food products (Cosgrove and others 1987; Neff and others 1993). Furthermore, Dimick (1982) reported the association between the activation of riboflavin and the degradation of dairy products. Vitamins such as tocopherol (Parkhurst and others 1968; Cillard and others1980; Niki and others 1984), -carotene (Matsushita and Terao1980; Palozza and Krinsky 1992), and ascorbic acid (Cort 1974;

Miller and Aust 1989) were reported to prevent or promote the oxidation. Light-induced oxidation of fluid milk has been well documented and discussed in several reviews (Forss 1979; Chen and Nawar 1991; Azzara and Campbell 1992).

However, the theories regarding light-induced oxidation of fluid milk are considered inapplicable to the photooxidation of ice cream because the composition (including the fat content), manufacturing process, and storage condition of ice cream are obviously different from that of fluid milk. Little is known about the mechanism of light-induced oxidation of milk fat in ice cream.

The present investigation expanded upon previous studies of photooxidation of milk to ice cream containing 14.25% milk fat. The objectives of the research were to determine the relation between the photooxidation of milk fat in ice cream and flavor deterioration, and to reveal the factors affecting the photooxidative stability of ice cream. These results can help improve the photooxidative stability of ice cream.

Materials and MethodsNGREDIENTS FOR MILK FAT USED IN THIS STUDY WERE OBTAINED

FROM different commercial sources in Australia, Hungary, and Japan. These materials were prepared with conventional

centrifugation, and the compositions are shown in Table 1. Commercial skim milk powder (Snow Brand Milk Products Co., Ltd., Tokyo, Japan) was used. The following were commercially

purchased and used as ingredients for the ice cream mix: glycerol monostearate (Rik- en Vitamin Co., Ltd., Tokyo, Japan)

as the emulsifier; mixture of locust bean gum, guar gum, and gelatin ( Taiyo Kagaku Co., Ltd., Yokkaichi, Japan) as the

stabilizer; -carotene (Roche Holding Ltd., Basle, Switzerland) as the coloring agent, and sugar (Dain- ippon Meiji Seito Co.,

Ltd., Tokyo, Japan). All reagents for analyti-cal experiments were of analytical grade.

Preparation of ice cream mixThe composition of the ice cream mix is shown in Table 2.

Raw materials—skim milk, milk-fat material, emulsifier, stabilizer, sugar, coloring agent, and water—were combined as shown in

1200 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 3, 2002 © 2002 Institute of Food Technologists

Sens

ory

and

Nutri

tive

Quali

ties

of Fo

od

Photooxidative stability of ice cream . . .Photooxidative stability of ice cream . . .

ay 1949). These experiments were duplicated. The contents of the tocopherol were measured by high-per-

Vol. 67, Nr. 3, 2002—JOURNAL OF FOOD SCIENCE 1201

Nr 7.od. The scores of Nr 7 exposed for 3 and 7 d were higher than

1202 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 3, 2002

Table 1—Composition of milk-fat materials used for ice cream samples (Nr 1 through Nr 7)

Table 2—Ice cream formulation

Content %Ice cream samples

NrFat%

Solids, non-fat%

Water% Fat 14.25

Solids, non-fat 11.501 40.0 4.8 55.2 Sugar 12.762 68.0 2.0 30.0 Emulsifier 0.253 78.0 4.0 18.0 Stabilizer 0.204 75.0 1.0 24.0 Coloring agent 0.065 69.0 4.0 27.0 Water 60.986 60.0 10.0 30.07 84.0 1.8 14.2

the table to obtain 100 kg of mix. All mixes were prepared with fat content set at 14.25%, and the concentration of non-fat milk solids was adjusted to 11.50% by the addition of skim milk and water. The raw materials were dissolved and mixed well in water and pasteurized at 80 C for 60 s. The ice cream mixes were

homogenized at a total pressure of 150 kg/cm2 and secondary pressure of50 kg/cm2 by using a homogenizer (Sanwa Machine Co., Inc., Nu-mazu, Japan).

Ice cream productionThese prepared ice cream mixes were aged overnight at 5 C,

then frozen in an ice cream freezer (APV Crepaco, Inc., Chicago, Ill., U.S.A.) to 5 C. The overrun of all samples was 70%. These frozen mixes were filled and packaged in 50-mL containers and kept at 20 C.

Extraction of oil fraction from milk-fat materialsThe milk-fat materials adopted in this study were dissolved in

n-hexane/diethyl ether (1:1, v:v) and then shaken strongly by a vortex mixer (MT-51, Yamato Scientific Co., Tokyo, Japan) for 3 min. The upper phase was collected and the solvent was removed by a roto-evaporator to obtain the oil fraction from the milk-fat materials (REI-N, Asahi Techno Glass Corp.).

Extraction of ice cream oil partThe whole cup of ice cream samples used for each analysis

was dissolved in n-hexane/diethyl ether (1:1, v:v) and then shaken strongly by a vortex mixer for 3 min. The upper phase was collected and the solvent was removed by a roto-evaporator to obtain the oil part from ice cream samples.

Light-exposing storage testThe light-exposing storage test was carried out for the ice

cream samples and for the oil fractions: (1) The ice cream samples (50 g of each) were packed in white paper containers with transparent polyethylene terephthalate caps. These samples were placed on shelves exposed to 650 l x fluorescent light from the top and kept at –20 C. At intervals of 0, 1, 2, 3, 5, and 7 d, we removed the ice cream samples and determined the peroxide values (PVs). The display case was illuminated by cool white fluorescent lamps mounted parallel to the shelves at a distance of50 cm from the samples. (2) The oil fractions (10 g of each) were kept in 7.2-cm-dia petri dishes and placed on shelves under

the same conditions. At intervals of 0, 3, and 7 d, we removed oil fraction samples and determined the PVs.

Photooxidative stability was evaluated by PV determined by the colorimetric ferric thiocyanate method (Chapman and Mack-






Sensory evaluation

Sensory evaluations of ice cream samples exposed to fluorescent light for 0-, 3-, and 7-d intervals were conducted by 6 trained panelists. Before evaluation, a 1-h training session was held to familiarize the panelists with the evaluation method. During the training session, samples that contained the oxidized off-flavor were presented to the panelists, and these panelists were instructed to estimate the characteristic identified as oxidized off-flavors. The samples used during training evaluation were taken from ice cream, both fresh and exposed to light for various times to obtain different intensities of oxidized flavor. In this session, panelists were also taught how to evaluate samples.

The trained 6 panelists evaluated the ice cream for intensity of oxidized flavor. Ice cream samples were served at –12 C in a50-mL capacity white paper cup. All samples were coded with random numbers, and all orders of serving were completely ran- domized. The ice cream samples were served at room temperature in partitioned booths illuminated with white fluorescent lights. Filtered water (21 C) was provided to cleanse the palate of panelists between the samples. Panelists were instructed also to rest between samples to avoid fatigue. The intensity of light- induced deterioration of the samples was scored on a 10-point scale. Scoring was from 1, very strong oxidized flavor, to 10, no flavor defected.

Fat anal ysis

The fat content of all milk-fat materials was measured by Roese-Gottlieb’s method (AOAC 1991). Free-fat content, which was regarded as fat outside the fat globules in ice cream, was measured as described by Noda (Noda and Shiinoki 1986). The fatty acid composition of the oil fraction was measured by gas liquid chromatography, as follows. An oil sample was transmethy- lated by potassium hydrate (KOH) to obtain the fatty acid methyl esters, which were dissolved in n-hexane and injected into the gas liquid chromatograph. The fatty acid composition was measured using the following equipment: Hewlett-Packard HP6890 series II (Hewlett-Packard, Palo Alto, Calif., U.S.A.); detector, flame-ionization detector (Hewlett-Packard); column, fused-sili- ca capillary column, DB-WAX (30 m, 0.25 i.d., 0.25 M [film], J & W Scientific, Folsom, Calif., U.S.A.); and carrier gas, helium.

Analysis of vitamins and minerals

The -carotene content in each oil fraction was measured by high-performance liquid chromatography under the following conditions: column, Shodex PSpak DS-613 (150 mm × 6.0-mm i.d., Showa Denko K.K., Tokyo, Japan); mobile phase, methanol/ n-hexane/benzene = 2:1:1; detection,

UV/VIS detector (UV-970, JASCO Corp., Hachioji, Japan) at a wavelength of 453 nm; column oven temperature, 60 C; flow rate, 0.8 mL/min.

Ice cream samples Storage period (d) of flavor scores were observed among samples Nr 2, 3, 4, 5, and 6.

Nr 0 3 7 These results indicated that milk-fat materials used for ice cream

1 7.67a 5.25a 4.50a preparation in this study led to different degrees of intensity for

2 8.67a 6.67ab 6.33bc photo-induced off-flavor.3 8.67a 6.50ab 5.67abc The quality of ice cream depends upon the source of basic in-4 8.58a 7.00ab 5.83abc

gredients, especially milk fat. An oxidized flavor in the milk fat5 8.75a 6.92ab 5.50ac

6 8.75a 7.00ab 6.33bc

7 9.00a 8.17b 7.42b sumer acceptability of ice cream (Abd EL-Rahman and others

Sensory and Nutritive Qualities of Food






Table 3—Time dependence of flavor score of ice creams exposed to 650 l × fluorescent light at – 20 C

those of other samples. And scores of Nr 1 exposed for 3 and 7 d were lower than those of other samples. Insignificant differences

could carry over into the ice cream and lowers the relative con-

Values followed by the same letters at same storage period are not significantly different atP < 0.05.

formance liquid chromatography under the following conditions: column, Zorbax NH2 (250 mm × 4.6-mm i.d., Hewlett-Packard, Palo Alto, Calif., U.S.A.); mobile phase, n-hexane/2-propanol = 49:1; detection, fluorescence detector (FP-920S, Jasco Corp., Hachioji, Japan) at a wavelength of Ex 298 nm and Em 325 nm; column oven temperature, 35 C; flow rate, 1.3 mL/min.

The contents of the ascorbic acid were measured by high-performance liquid chromatography under the following conditions: column, Nucleosil Si100 3 m (150 mm × 6.0-mm i.d., GL Sciences Inc., Tokyo, Japan); mobile phase, n-hexane/ethyl acetate/n- propanol/acetic acid = 40:30:2:1; detection, UV/VIS detector (UV-970, JASCO Corp., Hachioji, Japan) at a wavelength of 495 nm; column oven temperature, 25 C; and flow rate, 1.3 mL/min.

The contents of the riboflavin were measured by high-performance liquid chromatography under the following conditions: column, Cosmosil 5 C18 (150 mm × 4.6-mm i.d., Nacalai Tesque Co., Ltd., Kyoto, Japan); mobile phase, 10 mM of NaH2PO4 (pH =5.5) / methanol = 70:30; detection, fluorescence detector (F1100,

Hitachi Ltd., Tokyo, Japan) at wavelengths of Ex 445 nm and Em530 nm; column oven temperature, 40 C; and flow rate, 0.8 mL/min.

Minerals were identified and quantified by inductively cou- pled plasma (ICP) emission spectrometry (ICPS-8000, Shimadzu Corp., Ltd., Kyoto, Japan) ( JISC 1998).

Statistical analysisMeans obtained from flavor scores were subjected to analysis

of variance according to the Statistical Analysis System (SAS) (SAS Institute 1992). The probability for statistical significance was set at P < 0.05. The combined influence between peroxide formation of the oil part and riboflavin content was investigated with multiple regression analysis. Prior to this analysis, the average and standard deviation of variables were transformed to 0 and 1, respectively. This analysis was performed with SAS software.

Results and Discussion

Sensory evaluation of oxidized flavor after storageFlavor changes during the storage of ice cream samples,

which were prepared from 7 fat materials and exposed to fluorescence light, were determined by sensory evaluation. The total amount of fat content of all ice cream samples in this study was set to a definite percentage of 14.25% because fat content in a food influences both texture and flavor (Li and others 1997). Ta- ble 3 shows the results of sensory evaluation on the 7 ice cream samples for the storage period of 0, 3, and 7 d. The flavor score decreased as the storage period increased. This result

indicated an increase in intensity of oxidized flavor during the storage peri-






1997). From this report, the differences of flavor scores among ice cream samples stored 0 d in this study was suggested to be influenced by the differences in milk fat’s oxidized flavor. This result showed the importance of the initial quality of the starting raw materials, especially the milk fat, for the light-exposed product’s quality.

Milk-fat materials and light-induced oxidationThe photooxidative stability of ice cream samples prepared from 7

milk-fat materials was evaluated. After the samples were exposed to fluorescent light for storage periods of 0, 1, 2, 3, 5, and7 d, the oil fraction PV extracted from them was determined, as shown in Figure 1. These PVs increased with the increasing storage period. The PV of ice cream sample Nr 1 increased significantly faster than that of other samples, and those of samples Nr6 and Nr 7 increased insignificantly. After the samples were exposed to fluorescent light for the 7-d storage period, sample Nr 1 showed the highest PV, 6.8 meq/kg among the samples, and the PVs of samples Nr 6 and Nr 7 were as low as approximately 1.3 meq/kg. This result showed that ice cream could have different susceptibilities on the light-induced oxidation depending on the fat ingredients used in this study.

Figure 1—Time dependence of peroxide value of fat part in ice creams exposed to 650l × fluorescent light at –20 C. Samples: Nr 1; Nr 2; Nr 3; Nr 4; Nr 5; Nr 6;

r = 0.795) 3; Nr 4; Nr 5; Nr 6; Nr 7


and that of ice creams r = 0.367)



Table 4—Composition of oil fraction from milk-fat materials

Nr 1 Nr 2 Nr 3 Nr 4 Nr 5 Nr 6 Nr 7

Fatty acid composition (%)C4:0 1.9 1.8 1.8 2.0 1.5 1.9 1.9C6:0 1.5 1.6 1.5 1.6 1.4 1.5 1.6C8:0 1.0 1.2 1.0 1.1 1.1 1.1 1.1C10:0 2.4 2.9 2.6 2.5 2.6 2.7 2.8C12:0 3.0 3.6 3.3 3.0 3.2 3.3 3.4C14:0 11.1 11.8 10.8 10.8 10.5 10.6 11.2C14:1 1.0 1.0 1.1 0.9 0.9 0.9 1.0C15:0 1.3 1.3 1.3 1.1 1.1 1.1 1.2C16:0 31.9 29.8 31.7 29.6 28.7 30.3 31.3C16:1 1.5 1.6 2.0 1.7 1.8 1.6 1.5C18:0 13.2 11.6 10.2 12.4 12.6 11.6 11.5C18:1 21.5 22.3 23.4 24.1 25.6 24.1 22.9C18:2 2.0 2.2 3.1 2.2 2.5 3.9 3.2C18:3 1.6 2.0 1.4 1.9 1.9 1.0 1.0Oxidizabilitya 0.0563 0.06646 0.06368 0.06482 0.06812 0.0638 0.05658 -Carotene ( g/100 g) 426 589 456 474 607 326 114Tocopherol (mg/100 g) -Tocopherol 1.90 2.15 3.00 3.48 2.83 1.22 1.42 -Tocopherol nd 0.01 0.01 nd nd nd nd -Tocopherol 0.01 0.03 0.04 0.03 0.04 0.11 0.15 -Toc./ -Toc. 0.0053 0.0140 0.0133 0.0086 0.0141 0.0902 0.1056aCalculated by the following formula: 0.02 × oleic acid content(%) + linoleic acid content(%) + 2 × linolenic acid content(%)nd = not detected

Relationship between flavor score and generation of hydroperoxide

The relationships between flavor scores and PVs determined for ice cream samples were estimated as shown in Figure 2. The flavor score decreased with increasing peroxide values. And the correlation coefficient r was 0.795 (n = 21). Photooxidation of the oil part in milk was reported to affect flavor deterioration (Forss1979; Azzara and Campbell 1992). The result in this study suggested that the development of off-flavor in ice cream exposed to

fluorescent light may be due to photooxidation of milk fat in ice cream.

Photooxidative stability of oil fractionsThe photooxidative stability of the oil fraction extracted from

milk-fat materials used in this study was evaluated. The PV of the oil fraction increased with the increasing storage period as shown in Figure 3. The PV of Nr 3 exposed 7 d was higher than those of other samples. And the PVs of Nr 6 and Nr 7 exposed 7 dwere lower than those of other samples.

Sens

ory

and

Nutri

tive

Quali

ties

of Fo

od

r = 0.795) 3; Nr 4; Nr 5; Nr 6; Nr 7





Figure 2—Correlation between flavor score and peroxide values of fat part in ice creams exposed to 650l × fluorescent light at –20 C for 7 d (correlation coefficient, n = 21,

Figure 3—Time dependence of peroxide value of oil fraction extracted from milk-fat materials exposed to 650l × fluorescent light at –20 C. Samples: Nr 1; Nr 2; Nr



r = 0.795) 3; Nr 4; Nr 5; Nr 6; Nr 7




Table 5—Composition of hydrophilic substances of ice cream samples

Nr 1 Nr 2 Nr 3 Nr 4 Nr 5 Nr 6 Nr 7

Riboflavin (mg/100 g) 0.0945 0.0593 0.0455 0.0496 0.0535 0.0601 0.0438Ascorbic acid (mg/100 g) 0.775 0.198 nd nd nd nd ndMineral (mg/100 g)

Na 8.94 2.96 1.78 1.93 1.85 22.38 1.38K 27.83 12.61 7.15 7.06 6.85 13.10 4.94Ca 17.50 6.11 2.95 3.64 3.75 47.58 2.23Mg 1.67 0.70 0.39 0.43 0.46 2.40 0.32P 16.07 7.37 4.60 4.59 5.40 33.32 4.26Fe 0.04 0.04 0.03 0.04 0.03 0.06 0.04Zn 0.08 0.05 0.04 0.05 0.04 0.21 0.05Cu nd nd nd nd nd nd ndMn nd nd nd nd nd nd nd

nd = not detected

Figure 4 shows the correlation between the increased PVs ( PV ) of the ice cream oil parts and those of oil fractions exposed for 7 d. The numbers shown on the plots indicate the sample numbers. The PVs of these milk-fat materials’ oil fractions were 5 times higher than those of the corresponding ice cream samples’ oil parts under this experimental condition. A high correlation of PV was observed between milk-fat materials’ oil fractions and ice cream samples’ oil parts for samples Nr 2, 4, 5, 6, and 7 (r =0.935). However, samples Nr 1 and 3 did not belong to the high correlation described above. The PV of the oil parts in ice cream samples was relatively high compared with the oil fraction for sample Nr 1. On the contrary, PV was relatively low in ice cream for sample Nr 3 compared with the oil fraction. These results indicate that the photooxidative stability of ice cream depends on the oxidative stability of its oil part, but other factors mentioned later are affecting the photooxidative stability of ice cream.

Effect of milk-fat componentsPhotooxidative stability of milk has been reported to be af-

fected by the composition of fatty acid or vitamins in it (Cillard and others 1980; Cosgrove and others 1987; Olsen and Ashoor1987). These compositions are attributed to the seasonal differences in feeding conditions or processing conditions of several milk products, and so on (Norris and others 1973; Bassette and others 1983; Jensen and others 1999).

To investigate the factors affecting light-induced oxidation of the oil fraction of milk-fat materials, we determined the compositions of oil fractions. As shown in Table 4, the fatty acid composition and the contents of some oil-soluble vitamins, tocopherols, and -carotene, were determined. It is well known that the oxidative stability of saturated fatty acids > monounsaturated fatty acids > polyunsaturated fatty acids. Thus the oxidizability of these oil fractions, which were calculated on the basis of the unsaturated fatty acid composition (Cosgrove and others 1987), was also shown in Table 4.

Oxidizability = 0.02 × oleic acid content (%) + linoleic acid content (%) + 2 × linolenic acid content (%)


r = 0.795) 3; Nr 4; Nr 5; Nr 6; Nr 7




Figure 4—Correlation of peroxide values of oil fractions Figure 5—Correlation between peroxide values of oil fractions and oxidizability (correlation coefficient, n = 7,

cient, n = 7, r = 0.846) r = 0.634).


zen in the manufacturing process, in which processed milk-fat Dutton HJ, Schwab AW, Moser HA, Cowan JC. 1948. The flavor problem of soy-



Table 6—Free-fat contents and oxidizability of ice cream samples.

quencher of activated oxygen (Matsushita and Terao 1980; Goul- son and Warthesen 1999). However, the results showed that -

Ice cream samples Free-fat content/ Oxidizability carotene could adversely affect and lessen the photooxidative N o total fat content % rati o a stability for milk fat. A more precise investigation is required to

1 33.29 1.04 clarify the impact of -carotene.3 18.24 0.94 These results indicate that the photooxidative stability of the6 37.25 0.98 oil fraction depended on the composition of the oil-soluble vita-

7 28.10 0.93 aOxidizability ratio = oxidizability of free fat to oxidizability of total fat.

The influence of composition differences on light-induced oxidation was examined. To compare the susceptibility of the photooxidation of the oil fraction, the increasing rate of peroxide formation from 0 to 7 d was defined as PV (oil). The correlation coefficients between the PV (oil) of oil fractions and oxidizability, tocopherol composition, and -carotene concentration were determined.

The oxidizability values ranged narrowly from 0.056 to 0.068. The PV (oil) of the oil fractions and oxidizability showed low correlation (correlation coefficient r = 0.367), as shown in Figure 5. The effects of tocopherols’ composition on the PV (oil) of the oil fractions are shown in Figure 6. The amount of tocopherols affected the photooxidative stability of the oil fraction. The PV (oil) decreased with the increasing -tocopherol/ -tocopherol ratio with a high correlation (correlation coefficient r = 0.846). The results showed that -tocopherol is effective in obtaining photooxidative stability for milk fat, and supported previous research reporting that antioxidative activity of tocopherol increased in the order of < < < (Griewahn and Daubert 1948). Figure 7 shows the effect of -carotene content on PV (oil) of the oil fractions. The PV (oil) increased with increasing -carotene content, and the correlation coefficient (r) was 0.634. -Carotene wasreported to inhibit lipid photooxidation because of its ability as a

mins, such as tocopherol and -carotene; however, the influence of fatty acid compositions on the photooxidative stability of oil was lower under the conditions in this study.

Hydrophilic fraction of milk-fat materialsAnother factor affecting light-induced oxidation—the effect

of hydrophilic substances, such as riboflavin, ascorbic acid, and minerals—was investigated. Transition metals like Cu and Fe (Hegenauer and others 1979) and ascorbic acid (Parkhurst and others 1968) were reported to involve oil autooxidation. The influence of riboflavin on light-induced fat oxidation was especially important (Korycka-Dahl and Richardson 1978; Azzara and Campbell 1992). The compositions of these hydrophilic substances in ice cream samples are shown in Table 5. Ice cream sample Nr 1 shows the highest riboflavin content. Oxidation that involves riboflavin was presumed to progress in fluid milk as follows: First, riboflavin is reduced by light with the amino acid (Ko- rycka-Dahl and Richardson 1978). Reduced riboflavin is reoxi- dized to form a superoxide anion. Riboflavin is capable of generating singlet oxygen via the excited triplet state or superoxide anion. The photogeneration of singlet oxygen could lead to autooxidation of unsaturated fatty acid (Rawls and Santen 1970). Ice cream samples Nr 1 and 2 contained ascorbic acid, and other samples did not contain ascorbic acid. In this experiment, the influence of ascorbic acid on the photooxidation was not clear. Ice cream sample Nr 1 showed lower oxidative stability compared with the correlation with PV of oil fractions, as shown in Figure

Sens

ory

and

Nutri

tive

Quali

ties

of Fo

od

cient, n = 7, r = 0.846) r = 0.634).





Figure 6—Correlation between peroxide values of oil fractions and -tocopherol/ -tocopherol (correlation coeffi-

Figure 7—Correlation between peroxide values of oil fractions and -carotene content (correlation coefficient, n = 7,



cient, n = 7, r = 0.846) r = 0.634).




4. It was suggested that riboflavin could promote photooxidation in ice cream.

Among transition metals, Cu was known to act as a strong prooxidant (Dutton and others 1948). However, the amount of Cu in all ice cream samples was trace level (under 0.01 mg/100 g) to promote milk-fat oxidation (Renner 1983). Furthermore, sample Nr 6 contained the highest amount of transition metals among samples, had a low concentration of Fe (0.06 mg/100 g), and did not promote photooxidation. It was inferred from this result that the content of transition metals was so low that the con- tribution of metals to photooxidation of ice cream appears insignificant.

Combined influence of some factors on the photooxidation of ice cream

The combined influence of the photooxidative stability of the oil fraction of ice cream was investigated with multiple regression analysis. The combined influence between oxidizability and -tocopherol/ -tocopherol on the photooxidative stability of the oil fraction was determined. The -carotene content in milk-fat materials was dropped from the regression analysis because -carotene was added as a coloring agent in this ice cream mix, and the amount of -carotene carried over from milk-fat ingredients was too low in comparison with that of -carotene to affect the photooxidation of ice cream. Prior to the multiple regression analysis, all data were standardized. Through the standardization process, the average and standard deviations of valuables were transformed to0 and 1, respectively. The multiple linear model was:

PV (oil) = 0.05 × oxidizability – 0.83 × -tocopherol/ -tocopherol

where PV (oil) is the PV of the oil fraction increased during 7 d.In this regression equation, the coefficient of determination (R2)was 0.72. Thus 72% of the variation of data was explained by the combination of oxidizability and -tocopherol/ -tocopherol. The contributing proportion of oxidizability and -tocopherol/ -tocopherol on the photooxidative stability of the oil fraction was 2.0% and 69.9%, respectively. These results indicated that the tocopherol composition had more effect than the fatty acid composition on the photooxidative stability of oil fraction extracted from milk-fat materials.

Next, the combined influence of the susceptibility for photooxidation of the oil fraction and the riboflavin concentration was investigated with multiple regressions. The multiple linear model was:

PV (ice) = 0.47 × PV (oil) + 0.76 × riboflavin

where PV (ice) is the PV of ice cream, which increased over 7 d.

In this regression equation, the coefficient of determination (R2) was 0.71. Thus 71% of the variation of data was explained by the combination of the PV (oil) and the riboflavin content in ice cream. The contributing proportions of the PV (oil) and riboflavin content on the photooxidative stability of ice cream were17.6% and 53.7%, respectively.

This result suggested that the photooxidative stability of ice cream was influenced by the combination of riboflavin content and the susceptibility for photooxidation of the oil fraction.

Free-fat content dependence

Ice cream has a structure in which whipped air bubbles are stabilized by a network of solid milk fat. The ice cream mix is fro-

T


cient, n = 7, r = 0.846) r = 0.634).




globules are de-emulsified and a portion of milk fat, discharged from milk-fat globules, is present in free-fat form ( Thomas 1981). The free-fat content of several ice cream samples in this study was determined ( Table 6) to investigate the effect of free fat on photooxidative stability. Ice cream sample Nr 3 showed 18.24% free-fat content, which was lower than other ice cream samples. Ice cream sample Nr 3 showed high oxidative stability in spite of the low oxidative stability of the oil fraction, as shown in Figure 4. This result indicates that free-fat content affects the photooxidative stability of ice cream and suggests that the fat in milk globules has higher photooxidative stability than the free fat in ice cream. An insignificant difference of oxidizability, which was calculated on the basis of fatty acid composition, was observed between the oil fraction from milk-fat materials and free fat from ice cream samples. This indicates that the de-emulsification of the milk-fat globule to discharge free fat takes place with no specificity on fatty acid species. These results showed that fatty acids in free fat can be oxidized easier by light than can fatty acids in milk-fat globules, in spite of fatty acid compositions that are the same in both free fat and globules.

ConclusionsHE PHOTOOXIDATIVE STABILITY OF ICE CREAM SAMPLES PREPARED from 7 different milk-fat ingredients was investigated. We observed that

photooxidation of ice cream affected its oxidized flavor development. The combined influence of the photooxidative stability of the oil part

and riboflavin content on the photooxidative stability of ice cream was evaluated by multiple regression analysis. In this analysis, the

susceptibility for photooxidation of the oil part ( PV [oil]) and riboflavin content were identified and confirmed as important

attributes for the photooxidative stability of ice cream. The susceptibility of photooxidation of the oil part was influenced by the oxidizability of

fat-ty acid in the fat ingredient and tocopherol composition.

The results in this study suggested that vitamin concentration was important to the composition of ice cream, and free-fat content in ice cream was important to structure. The fatty acid composition and the concentration of vitamins in milk fat vary widely because of differences in dietary intake and genetic differences between cows. These also are influenced by the season, breed, lactation period, and other factors (Norris and others 1973; Hart- man and Dryden 1974; Jensen and others 1999). This result can help improve the photooxidative stability of ice cream by improv- ing the selection of ingredients and preparation conditions.

ReferencesAbd El-Rahman AM, Shalabi SI, Hollender R, Kilara A. 1997. Effect of milk fat fractions

on the sensory evaluation of frozen desserts. J Dairy Sci 80(9):1936-1940.

[AOAC] Association of Official Analytical Chemists. 1991. Official method of analysis. 16th ed. Vol. II. AOAC Official Method 920.111. Arlington, VA: Associ- ation of Official Analytical Chemists.

Azzara CD, Campbell LB. 1992. Off-flavors of dairy products. In: Charalambous G, editor. Off-flavors in Foods and Beverages. Amsterdam: Elsevier Science Publishers. P 329-374.

Bassete B, Fung DYC, Roberts H. 1983. Effect of pasteurization temperature on susceptibility of milk to light-induced flavor. J Food Prot 46:416-419.

Chapman RA, Mackay K. 1949. The estimation of peroxides in fats and oils by the ferric thiocyanate method. J Am Oil Chem Soc 26(7):360-363.

Chen ZY, Nawar WW. 1991. Role of milk fat globule membrane in autoxidation of milk fat. J Food Sci 56(2):398-401, 426.

Cillard J, Cillard P, Cormier M. 1980. Effect of experimental factors on the prooxidant behavior of -tocopherol. J Am Oil Chem Soc 57(8):255-261.

Cort WM. 1974. Antioxidant activity of tocopherols, ascorbyl palmitate, and ascor-bic acid and their mode of action. J Am Oil Chem Soc 51(7):321-325.

Cosgrove JP, Church DF, Pryor WA. 1987. The kinetics of the autoxidation of polyunsaturated fatty acids. Lipids 22(5):299-304.

Dimick PS. 1982. Photochemical effects on flavor and nutrients of fluid milk. CanInst Food Sci Technol J 15(4):247-256.

Sens

ory

and

Nutri

tive

Quali

ties

of Fo

od



bean oil. 4. Structure of compounds counteracting the effect of prooxidant metals. J Am Oil Chem Soc 25(11):385-388.

Forss DA. 1979. Mechanisms of formation of aroma compounds in milk and milk products. J Dairy Res 46:691-706.

Goff HD, Kinsella JE, Jordan WK. 1989. Influence of various milk protein isolates on ice cream emulsion stability. J Dairy Sci 72(2):385-397.

Goulson MJ, Warthesen JJ. 1999. Stability and antioxidant activity of beta carotene in conventional and high oleic canola oil. J Food Sci. 64(6):996-999.

Griewahn J, Daubert BF. 1948. Delta-tocopherol as an antioxidant in lard. J AmOil Chem Soc 25(1):26-27.

Guinard J-X, Zoumas-Morse C, Mori L, Uatoni B, Panyam D, Kilara A. 1997. Sugar and fat effects on sensory properties of ice cream. J Food Sci 62(5):1087-1094.

Hartman AM, Dryden LP. 1974. The vitamins in milk and milk products. In: Webb BH, Johnson AH, Alford JA, editors. Fundamentals of dairy chemistry. Westport,CT: Avi Publishing Company. P 325-401.

Hegenauer J, Saltman P, Ludwig D, Ripley L, Bajo P. 1979. Effect of supplemental iron and copper on lipid oxidation in milk. 1. Comparison of metal complexes in emulsified and homogenized milk. J Agric Food Chem 27(4):860-867.

[ JISC] Japan Industrial Standards Committee. 1998. Testing methods for industrial wastewater ( JISK 0102). Tokyo: Japan Industrial Standards Committee.

Jensen SK, Johannsen AKB, Hermansen JE. 1999. Quantitative secretion and maximal secretion capacity of retinol, -carotene and -tocopherol into cows’ milk. J Dairy Res 66:511-522.

Korycka-Dahl M, Richardson T. 1978. Photogeneration of superoxide anion in serum of bovine milk and in model systems containing riboflavin and amino acids. J Dairy Sci 61(4):400-407.

Li Z, Marshall R, Heymann H, Fernando L. 1997. Effect of milk fat content on flavor perception of vanilla ice cream. J Dairy Sci 80(12):3133-3141.

Matsushita S, Terao J. 1980. Singlet oxygen-initiated photooxidation of unsaturated fatty acid esters and inhibitory effects of tocopherols and -carotene. In: Simic MG, Karel M, editors. Autoxidation in food and biological systems. NewYork: Plenum Press. P 27-44.

Miller DM, Aust SD. 1989. Studies of ascorbate-dependent, iron-catalyzed lipid peroxidation. Arch Biochem Biophys 271(1):113-119.

Neff WE, Mounts TL, Rinsch WM, Konishi H. 1993. Photooxidation of soybean oils

as affected by triacylglycerol composition and structure. J Am Oil Chem Soc70(2):163-168.

Niki E, Saito T, Kawakami A, Kamiya Y. 1984. Inhibition of oxidation of methyl linoleate in solution by vitamin E and vitamin C. J Biol Chem 259(7):4177-4182.

Noda M, Shiinoki Y. 1986. Microstructure and rheological behavior of whipping cream. J Texture Stud 17:189-204.

Norris GE, Gray IK, Dolby RM. 1973. Seasonal variations in the composition and thermal properties of New Zealand milk fat. J Dairy Res 40:311-321.

Ohmes RL, Marshall RT, Heymann H. 1998. Sensory and physical properties of ice creams containing milk fat or fat replacers. J Dairy Sci 81(5):1222-1228.

Olsen JR, Ashoor SH. 1987. An assessment of light-induced off-flavors in retail milk. J Dairy Sci 70(7):1362-1370.

Palozza P, Krinsky NI. 1992. -carotene and -tocopherol are synergistic antiox- idants. Arch Biochem Biophys 297(1):184-187.

Parkhurst RM, Skinner WA, Sturm PA. 1968. The effect of various concentrationsof tocopherols and tocopherol mixtures on the oxidative stability of a sample of lard. J Am Oil Chem Soc 45(10):641-642.

Rawls HR, Santen PJV. 1970. A possible role for singlet oxygen in the initiation of fatty acid autoxidation. J Am Oil Chem Soc 47(4):121-125.

Renner E. 1983. Milk and dairy products in human nutrition. München: W-GmbH, Volkswirtschaftlicher Verlag. p 333-338.

SAS Institute. 1992. SAS/STAT user’s guide. Version 6.04. Cary, N.C.: SAS InstituteInc.

Schmidt KA, Smith DE. 1989. Effects of varying homogenization pressure on the physical properties of vanilla ice cream. J Dairy Sci 72(2):378-384.

Thomas EL. 1981. Structure and properties of ice cream emulsions. Food Technol35(1):41-48.

MS 20000901 Submitted 9/5/00, Accepted 11/23/01, Received 3/11/02

Authors Shiota, Ikeda, Konishi, and Yoshioka are with the Technology and Research Institute, Snow Brand Milk Products Co., Ltd., 1-1-2 Minamidai, Kawagoe, Saitama 350-1165, Japan. Direct inquiries to author Shiota (E- mail: [email protected]).

Documents

7. Fotooxidacion en Helados de Crema