EFFECT OF INULIN AND AGAVE FRUCTANS ADDITION ON THE RHEOLOGICAL, MICROSTRUCTURAL AND SENSORY PROPERTIES OF REDUCED FAT FERMENTED LACTIC BEVERAGES

1C. Lobato-Calleros, 1G. Crispín-Isidro, 2H. Espinosa-Andrews1Departamento de Preparatoria Agrícola y Posgrado en Ciencia y Tecnología Agroalimentaria, Universidad Autónoma Chapingo, Km. 38.5 Carretera México –Texcoco, Texcoco, Edo. México 56230, México

2Unidad de Tecnología Alimentaria, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A.C. Av. Normalistas #800, Guadalajara, Jalisco 44270, México

ABSTRACTThe composition, rheology, microstructure, and sensory acceptability of reduced-fat fermented lactic beverages (RF and RI) added with different concentrations (2, 4 or 6 % w/w) of medium chain inulin (I) or agave fructans (F) were evaluated in comparison with those showed by a full-fat (FC) and a reduced-fat (RF) control beverages. Scanning electron micrographs showed that the casein micelles forming the protein network of the RF beverages were covered with amorphous structures attributed to fructans chains; while the protein network of the RI beverages contained intermingled but independent inulin gelled structures. As higher was the concentration of inulin or fructan higher was the viscoelastic response of the protein network of the RF and RI beverages. RI 6, RI4, and RF6 beverages displayed rheological and sensory characteristic comparable with those of the FC beverage.

INTRODUCTION

Metabolic syndrome is a combination of three or more of the following: overweight/obesity, hypertension, disturbances of lipid and carbohydrate metabolism, elevated triacylglyceride concentrations, and low levels of high-density lipoproteins (HDL) in blood. It has been established that is possible to prevent or delay metabolic syndrome through lifestyle and nutritional changes. For example, fiber dietary intake may modulate parameters associated with the control of the metabolic syndrome because of its prebiotic and soluble dietary fiber properties.

Fructans extracted from chicory roots (inulin-type fructans) and Agave tequilana are able to promote the production of satietogenic/incretin peptides in the lower part of the gut, with promising effects on glucose metabolism, body weight and fat mass development. Inulin has been used to replace fat while improving taste and mouthfeel of dairy products.

In contrast, there are no reports in the literature dealing with the effect of agave fructans on the physicochemical and sensory characteristics of different types of foods. The branched structure of agave fructans may confer different functional properties than those reported for linear fructans of inulins, giving way to new technological applications.

The objective of this study was to evaluate and contrast the effect of adding agave fructans and inulin to reduced fat fermented lactic beverages (FLB) upon their composition, rheology, microstructure, and sensory acceptability.

MATERIALS AND METHODS

Fermented lactic beverages variationsFull-fat control (FC; 2.6 % w/w milk fat); reduced-fat control (RC; 1.3 % w/w milk fat); and six reduced-fat beverages (1.3 % w/w milk-fat) containing medium chain inulin (I) or Agave fructans (F) (2.0, 4.0 or 6.0 % w/w) yielding RI2, RI4, RI6, RF2, RF4, and RF6 beverages, respectively. All of the variations had 10.3 % w/w of non-fat milk solids and 2.8 % w/w of protein.

Fermented lactic beverages characterizationChemical composition and syneresisRheological properties. Amplitude sweeps (0.01–100 % strain, 1 Hz) and frequency sweeps (0.01-100 Hz,

0.2 % strain). (Physica MCR 301 Shear Rheometer, Anton Paar, Messtechnik, Stuttgart, Germany). G’ and G” values were obtained from the equipment softwareMicrostructure (Scanning Electron Microscopy) Sensory attributes (acidity, flavor, creaminess, sweetness, granularity, viscosity) and overall acceptability using a nine-point hedonic scale (1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 = dislike very little, 5 = neither like nor dislike, 6 = like a little, 7 = like moderately, 8 = like very much, and 9 = like extremely)

RESULTS AND DISCUSSION

Chemical composition and syneresis of the fermented lactic berveragesThe FC beverage had a fat content that was higher (p ≤ 0.05) than that of the RC, RF and RI beverages (Table 1). All of the FLB variations showed similar (p > 0.05) protein content, as this was standardized at 2.8 % w/w. Increasing F and I levels increased total solids values of the FLB. In general, the RF and RI beverages exhibited lower values of syneresis than those exhibited by FC and RC beverages (Table 1).

Table 1. Chemical composition and syneresis of the fermented lactic beveragesFLB code Fat

(%)Protein

(%)Total solids

(%)Acidity

(°D)Syneresis

(%)

FC 2.7 ± 0.1b 2.9 ± 0.1a 17.4 ± 0.2ab 78.5 ± 0.7a 9.9 ± 0.6c

RC 1.3± 0.0a 2.7± 0.1a 16.9 ± 0.3a 83.0 ± 1.4ab 13.5 ± 1.5d

RF2 1.3± 0.0a 2.9 ± 0.3a 18.3 ± 0.4b 85.0 ± 1.4b 5.0 ± 0.4ab

RF4 1.3± 0.0a 2.8 ± 0.1a 22.1 ± 0.1de 86.0 ± 1.4b 3.7 ± 0.3ab

RF6 1.3± 0.0a 3.0 ± 0.3a 22.6 ± 0.6e 85.5 ± 2.1b 2.6 ± 0.2a

RI2 1.3± 0.0a 2.9 ± 0.0a 20.1 ± 0.1c 86.0 ± 1.4b 9.2 ± 0.9c

RI4 1.3± 0.1a 2.9 ± 0.0a 20.9 ± 0.4cd 84.0 ± 1.4ab 5.3 ± 0.5b

RI6 1.3 ± 0.0a 3.0 ± 0.0a 22.5 ± 0.4e 86.5 ± 0.7b 5.1 ± 0.1ab

FC: full-fat beverage control; RC: reduced-fat beverage control; RF and RI: reduced-fat beverages containing agave fructans or inulin (2, 4 or 6 % w/w), respectively. a,b,c,d,e: different superscripts within the same column indicate that the means differ significantly (p ≤ 0.05).

Microstructure of the fermented lactic beveragesThe microstructure of FC and RC beverages can be observed from the SEM micrographs (Fig. 1). FC microstructure (Fig. 1a) was mainly composed by aggregates and chains of casein forming three-dimensional networks, in which originally fat droplets, whey and lactic bacteria were trapped. The protein network of RC (Fig. 1b) was less dense, more open, and with more void spaces than that of the FC as consequence of smaller fused casein micelles aggregates, probably due to lower number of fat globules acting as linking protein agents.

The microstructure of the RF and RI beverages was formed by protein networks with differing structures between them and respect to those of the FC and RC beverages (Figs. 2 and 3). The RF beverages microstructure (Fig. 2) was composed by chains of fused casein micelles covered by an amorphous material attributed to fructans chains. As higher was the F concentrations more uniformly were covered the micelle caseins and more compact was the resulting protein network.

The RI beverages microstructure (Fig. 3) was characterized by the presence of apparently inulin gelled structures, intermingled but forming independent structures to the protein network. As higher was the I concentration more numerous gelled particles were observed into the protein network. It has been informed that the capability of inulin for gel formation and the subsequent gel strength is dependent of its polymerization degree; as higher is the long chain greater propensity of inulin to form gelled structures; in contrast, small chains remains soluble.

Rheological properties of the fermented lactic beverages

The variations of G and G with frequency for the FLB are shown in Fig. 4. Independently of their ′ ′′composition, the FLB exhibited a storage modulus characterized by showing a slightly increase in gradient with frequency. In all cases the G and G values corresponded to a weak gel structural ′ ′′network, where G was always greater than G in the range of frequencies studied. Although, the ′ ′′development of G and G with frequency was qualitatively similar for the eight variations of FLB, ′ ′′differences between the G’ and G’’ values at a same frequency were observed. Thus, at 1 Hz of frequency the G’ values of the FC (69.8 Pa) beverage was no significantly different from those of RI 6 (84.9 Pa), RI4 (63.2 Pa), and RF6 (55.25 Pa). The G’’ values for these FLB followed a similar trend.

0.01 0.1 1 10 1001

10

100

G' [P

a]

Frequency [Hz]

FC RC RF

2

RF4

RF6

RI2

RI4

RI6

0.01 0.1 1 10 1001

10

100

G'' [Pa]

Frequency [Hz]

CF RC RF

2

RF4

RF6

RI2

RI4

RI6

Fig. 4. Variation of the storage modulus (G’) and loss modulus (G’’) of the fermented lactic beverages as a function of frequency.

Sensory evaluation of the fermented lactic beverages

The great majority of the sensory attributes (acidity, creaminess, sweetness, granularity, and viscosity) of the reduced-fat FLB were perceived as similar (p > 0.05) from those showed by the FC beverage (Table 2). In contrast, the flavor and overall acceptability of the RF4 received a higher acceptability scores than those of the FC beverage.

Table 2. Sensory acceptability scores of the fermented lactic beveragesFLB code

Acidity Creaminess Sweetness Granularity Flavor Viscosity Overall acceptability

CF 7.0 ± 1.7ab 7.6 ± 1.3abc 7.1 ± 1.9ab 7.5 ± 1.5ab 7.2 ± 2.0ab 7.7 ± 1.1ab 7.5 ± 1.8ab

RC 7.3 ± 1.7ab 7.5 ± 1.5abc 6.9 ± 1.8a 7.5 ± 1.4ab 7.3 ± 1.7ab 7.4 ± 1.4ab 7.4 ± 1.7ab

RF2 6.7 ± 1.8a 7.1 ± 1.6ab 6.6 ± 1.8a 7.7 ± 1.4ab 6.7 ± 1.8a 7.0 ± 1.7a 6.9 ± 2.0a

RF4 7.9 ± 1.6 b 7.3 ± 1.4b 8.0 ± 1.6 b 8.2 ± 1.6b 8.4 ± 1.3c 8.0 ± 1.4b 8.5 ± 1.6 c

RF6 7.4 ± 1.3ab 7.3 ± 1.3ab 7.5 ± 1.5ab 7.5 ± 1.3ab 7.6 ± 1.7abc 7.1 ± 1.3a 7.8 ± 1.5bc

RI2 7.5 ± 1.5ab 7.7 ± 1.4bc 8.0 ± 1.3b 7.6 ± 1.3ab 8.1 ± 1.3bc 7.7 ± 1.3ab 8.0 ± 1.3bc

RI4 7.1 ± 1.7ab 6.9 ± 1.6a 7.0 ± 1.9ab 7.3 ± 1.5a 6.9 ± 1.9a 6.9 ± 1.8a 6.6 ± 1.7a

RI6 7.1 ± 1.8ab 7.6 ± 1.2abc 7.3 ± 2.0ab 7.0 ± 1.8a 7.3 ± 2.0ab 7.3 ± 1.4ab 7.3 ± 1.7ab

FC: full-fat beverage control; RC: reduced-fat beverage control; RF and RI: reduced-fat beverages containing agave fructans or inulin (2, 4 or 6 % w/w), respectively. a,b,c: different superscripts within the same column indicate that the means differ significantly (p ≤ 0.05).

CONCLUSIONES

In this work, it was established that reduced-fat fermented lactic beverages manufactured from reconstituted partially skim milk and Agave fructans (6 % w/w) or medium chain inulin (4 and 6 % w/w) emulated the rheological and sensory characteristics of its full-fat counterpart, despite their completely different structural arrangements. Fructans chains were completely integrated unto the protein network increasing its strength and strain resistance; while inulin chains formed secondary gelled structures that contributed to the mechanical behavior of the protein network. Additionally, syneresis propensity of the reduced-fat fermented lactic beverages containing inulin or Agave fructans was in general lower than that of the full-fat fermented lactic beverage.

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Fig. 3. Scanning electron micrographs of the reduced-fat lactic beverages containing medium chain inulin (I): (a) RI2 (with 2 % w/w of I); (b) RI4 (with 4 % w/w of I); and RI6 (with 6 % w/w of I). Magnification is 10 000×, scale bar=1 m.

a b c

Fig. 2. Scanning electron micrographs of the reduced-fat lactic beverages containing Agave fructans (F): (a) RF2 (with 2 % w/w of F); (b) RF4 (with 4 % w/w of F); and RF6 (with 6 % w/w of F). Magnification is 10 000×, scale bar=1 m.

a b c

Fig. 1. Scanning electron micrographs of the FLB beverages control: (a) full-fat (FC) and (b) reduced-fat (RC). Magnification is 10 000×, scale bar=1 m.

a b