ORIGINAL PAPER

Stability Modeling of Red Pigments Producedby Monascus purpureus in Submerged Cultivationswith Sugarcane Bagasse

Silvana Terra Silveira & Daniel Joner Daroit &Voltaire Sant’Anna & Adriano Brandelli

Received: 22 August 2011 /Accepted: 14 October 2011 /Published online: 3 November 2011# Springer Science+Business Media, LLC 2011

Abstract Monascus purpureus red pigments were producedin submerged cultivations employing sugarcane bagasse(SB) as carbon source in combination with variousnitrogen sources. Peptone and soy protein isolate (SPI)as nitrogen sources generated the best pigment yields.NH4Cl has not supported high pigment production. Redpigments produced using SB and SPI as growth substrateswere submitted to temperature and pH stability analysis.Data from thermal pigment degradation were fitted tofive mathematical models, and a first-order equationwas accepted as the best one to describe color decay.Red pigments showed high stability at low temperatures(30–60 °C) and at near-neutrality pH values (6.0–8.0)when compared to that at high temperatures (above60 °C) and at acidic pH values (4.0–5.0). Monascuspigments produced using a low-cost agroindustrial waste(SB) as carbon source could be utilized as colorants infoods and foodstuffs manufactured under mild processconditions.

Keywords Monascus . Pigments . Sugarcane bagasse .

Thermal stability . Kinetic modeling

Introduction

There is a growing tendency in the utilization of naturalingredients by the food industry, reflecting the concern ofthe consumers to the use of synthetic compounds. The useof natural food colorants is of particular interest sincevarious synthetic pigments have been associated with toxiceffects in foods (Sabater-Vilar et al. 1999; Mapari et al.2005). In comparison to colorants extracted from plant andanimals, microorganisms are more attractive sources ofpigments since they pose no seasonal impediments andcould be produced in high yields (Carvalho et al. 2006). Inthis sense, representatives of the fungal genus Monascusproduce well-known pigments that are employed forcenturies as food colorants in eastern countries. Thesepigments are synthesized as secondary metabolites by thepolyketide pathway, and at least six pigment structuresare recognized: monascorubramine and rubropuctamine(red pigments), monascorubrin and rubropunctatin (orangepigments), and monascin and ankaflavin (yellow pigments)(Dufossé et al. 2005; Mapari et al. 2005).

Although Monascus pigments are usually producedthrough solid-state processes, submerged cultivations areattractive alternatives that can benefit the production ofmany secondary metabolites (Panda et al. 2010). Insubmerged cultivations, the control of the process is simplerand easier, resulting in reduction of both cultivation timesand production costs (Domínguez-Espinosa and Webb2003). The use of agroindustrial residues is an increasingtrend in biotechnological processes since the utilization ofthese low-cost wastes as substrates for production ofmicrobial metabolites, besides reflection on final productcosts, represents a way of waste management (Daroit et al.2007; Silveira et al. 2008).

S. T. Silveira :D. J. Daroit :V. Sant’Anna :A. BrandelliLaboratório de Bioquímica e Microbiologia Aplicada,Departamento de Ciência de Alimentos,Universidade Federal do Rio Grande do Sul,Porto Alegre, Brazil

A. Brandelli (*)ICTA-UFRGS,Av. Bento Gonçalves 9500,91501-970 Porto Alegre, RS, Brazile-mail: abrand@ufrgs.br

Food Bioprocess Technol (2013) 6:1007–1014DOI 10.1007/s11947-011-0710-8

Stability evaluations are essential when assessing thecommercial/industrial potential of microbial metabolites(Sant’Anna et al. 2010). Particularly, knowledge onpigment degradation at different processing conditions isof importance from a technological viewpoint aiming foodapplications. During heat processing, a complex networkof reactions might occur, resulting in the destabilizationof a biomolecule. Mathematical models, consisting ofequations that provide an output based on a set inputdata, represent a powerful and concise way to expressphysical behavior in mathematical terms (van Boekel2008). Therefore, prediction of metabolite degradation/inactivation is feasible by applying adequate models andby performing thermodynamic studies. Several kineticequations have been proposed to model the thermaldegradation of food compounds, and some are presentedin Table 1.

In this context, this study presents the production ofMonascus purpureus pigments through submerged cultiva-tions employing sugarcane bagasse as carbon source incombination with various nitrogen sources. Subsequently,the stability pattern of the red pigments towards tempera-ture and pH was described, and thermal degradation wasevaluated using different kinetic models.

Materials and Methods

Microorganism

M. purpureus NRRL 1992 was used for pigment productionin this study. Cultures of this microorganism weremaintained on Sabouraud agar plates at 4 °C and subculturedperiodically.

Media and Culture Conditions for Pigment Production

Organic (peptone, soy protein isolate, soy bran, and cheesewhey powder) and inorganic (NH4Cl) nitrogen sourceswere screened in combination with sugarcane bagasse(carbon source) for pigment production by M. purpureusin submerged cultivations. Culture medium consisted ofsugarcane bagasse (20 g/L), organic (5 g/L) or inorganic

(2.5 g/L) nitrogen source, K2HPO4 (5.0 g/L), KH2PO4

(5.0 g/L), MgSO4·7H2O (0.1 g/L), CaCl2 (0.025 g/L),ZnSO4·7H2O (0.01 g/L), and MnSO4 (0.01 g/L). The initialpH of the medium was adjusted to 6.0 before autoclaving(121 °C for 15 min).

A conidial and mycelial suspension (O.D.620 of 0.4) ofM. purpureus was inoculated at 1% (v/v) in 250-mLErlenmeyer flasks containing 50 mL of medium. Inoculumwas prepared as described elsewhere, from 12-–14-day-oldcultures (Daroit et al. 2007). The inoculated flasks wereincubated at 27±3 °C on a rotary shaker at 125 rpm for upto 14 days.

Pigment Estimation

At the end of cultivation, or at defined intervals, aliquots of1 mL were withdrawn and centrifuged (10,000×g for5 min), and the supernatant was used for pigmentestimation. Only extracellular pigments were consideredin this study.

The analysis of red pigment production was done bymeasuring the absorbance of culture supernatants at 500 nmusing a spectrophotometer (Shimadzu UVmini-1240) andtaking the dilution factor of the samples into consideration.Results were expressed as absorbance units per milliliter(UA500/mL). Alternatively, analysis of the absorbancespectra (380–600 nm) of the aqueous pigment solutionswas performed.

Evaluation of Pigment Stability

For thermal stability tests, pigment solutions were incubatedat 30, 40, 60 or 80 °C from 0 to 360 min at pH 6.0. ForpH stability studies, pigment solutions of different pHvalues (4.0–8.0) were incubated at 80 °C from 0 to180 min. Also, pigment stability was evaluated afterautoclave treatment (121 °C for 15 min). The buffersolutions used were 0.2 M sodium citrate–phosphate (pH4.0, 5.0, and 6.0) and 0.2 mol/L sodium phosphate (pH7.0 and 8.0). In all these tests, pigment measurement wasperformed as described in the previous section andexpressed as percentage of the absorbance observed attime zero (control; 100%).

Table 1 Kinetic equationsemployed to evaluate thermaldegradation of M. purpureusred pigments

Model Equation (no.) References

First-order AA0

¼ exp �ktð Þ (1) Ludikhuyze et al. 1999

Weibull distribution AA0

¼ exp �btnð Þ (2) Weibull 1951

nth order AA0

¼ A01�n þ n� 1ð Þ � kt

� �1= 1�nð Þ(3) Shalini et al. 2008

Two-fraction AA0

¼ a� exp �kLtð Þ þ 1� að Þ � exp �kRtð Þ (4) Chen and Wu 1998

Fractional conversion AA0

¼ Ar þ A0 � Arð Þ � exp �ktð Þ (5) Rizvi and Tong 1997

1008 Food Bioprocess Technol (2013) 6:1007–1014

Statistical Analysis for Kinetic Modeling of ThermalDegradation

Experimental data of residual color (UA500/mL) for thermaldegradation through time were fitted to kinetic modelspresented in Table 1. In the equations, A/A0 represents theresidual absorbance (500 nm) at time t (min), and k (min−1)is the inactivation rate constant at a given temperature.The values of b and m in the Weibull model (Eq. 2) arethe shape and scale factors of the distribution curve,respectively. In the nth-order model (Eq. 3), n is the orderof the reaction. In the parallel models (Eqs. 4 and 5), theresidual color of possible “labile” and “resistant” pigmentfractions are represented by AL and AR, respectively,whereas kL and kR are the correspondent first-orderreaction rate constants for each fraction, respectively.Coefficient a in Eq. 4 represents the absorbance of thethermolabile pigment group in relation to the totalabsorbance.

The analysis was performed by both statistical and physicalcriteria. Coefficient of determination (r2), chi-square (χ2),and standard error of means (S.E.M.) were the statisticalcriteria evaluated. These criteria have been used succesfullyto compare the kinetics of thermal inactivation models ofseveral bioactive compounds (Corradini and Peleg 2004;Shalini et al. 2008; Sant’Anna et al. 2010).

Calculation of χ2 is done by the equation:

#2 ¼P

ameasured � apredicted� �2

n� pð Þ ð6Þ

SEM is defined as:

SEM ¼P

ameasured � apredicted� �2

ffiffiffin

p ð7Þ

where n is the number of observations and p the number ofparameters.

The model with the lowest χ2 and SEM and higher r2 forthe residual pigmentation is the best choice for modelingthe loss of the pigment through processing time (Sant’Annaet al. 2010). Estimation of negative kinetic parameters is aphysical criterion for rejection of a model.

Rsesults and Discussion

Sugarcane bagasse (SB) is an agro-industrial residueproduced in high amounts, mainly by the sugar and ethanolindustries. This residue is generated after the crushing andextraction of the juice from sugarcane and consists ofapproximately 50% cellulose, 25% hemicellulose, and 25%lignin. SB was already reported as a promising substrate for

the production of value-added products such as enzymes,among other biotechnological applications (Pandey et al.2000).

The production of M. purpureus red pigments using SBas carbon source, in combination with various nitrogensources, was investigated. The presence of inorganicnitrogen source (NH4Cl) had not supported red pigmentproduction (Fig. 1). Nevertheless, Fenice et al. (2000)reported that higher pigment production by M. purpureusstrain C322 was achieved in NH4Cl-containing medium.Peptone and soy protein isolate (SPI) were the best nitrogensources for red pigment production (Fig. 1). In peptone-containing medium, maximum red pigment productionwas detected at the 7th day of cultivation (2.820 UA500/mL),after which a descending trend on absorbance measurementat 500 nm was observed. With SPI as nitrogen source, redpigment concentration continued to grow until the end of thecultivation period, reaching 3.380 UA500/mL at day 14(Fig. 1). In this case, it is important to mention that despitethe pigment accumulation in the cultivation media, asubstantial drop on pigment productivity occurred at the14th day of cultivation (0.241 UA500/mL day) whencompared to that observed at day 9 (0.319 UA500/mL day),indicating that cultivations which developed for more than9 days adversely affect the final pigment yield.

Soy bran and cheese whey powder presented intermediateeffects on pigment production, probably because of theirlower organic nitrogen availability when compared to peptoneand SPI. Particularly, cheese whey concentrate powders have10–40% of protein (Heino et al. 2007) whereas SPI containsapproximately 90% of crude protein (Lusas and Riaz 1995).Since SPI has a lower cost when compared to peptone, it

Fig. 1 Red pigment production by M. purpureus through submergedcultivations with sugarcane bagasse (20 g/L) and different organic(5 g/L) and inorganic (2.5 g/L) nitrogen sources. Filled square, SBplus soy protein isolate; open square, SB plus peptone; filled triangle,SB plus cheese whey powder; filled diamond, SB plus soy bran;multiplication symbol, SB plus NH4Cl. Each point is the mean ± S.E.M. of duplicate cultivations and two pigment estimations for eachcultivation

Food Bioprocess Technol (2013) 6:1007–1014 1009

could be considered as a potential nitrogen source forproduction of important biotechnological products. Collec-tively, these results imply that both the presence and thecontent of organic nitrogen in the culture media are criticalparameters for high pigment production by M. purpureusNRRL 1992. Accordingly, the organic nitrogen source(peptone) was reported to be the most significant variablefor pigment production by this strain using grape waste ascarbon source (Silveira et al. 2008) and, generally, organicnitrogen sources are preferred for pigment production byMonascus species (Pastrana et al. 1995; Dufossé et al. 2005).Specifically, the production of rubropunctatin by Monascuspilosus was reported to be dependent on the component(s)of peptone (Miyake et al. 2008). Nimnoi and Lumyong(2011) tested the pigment production by M. purpureus onagricultural products, reaching best production on cornmeal as substrate.

Spectral analysis of pigments produced by M. purpureusNRRL 1992 shows absorbance peaks at 420–424 and500–503 nm (Fig. 2, line A). Similarly, the absorptionspectra of extracellular pigments produced by Monascussp. KB9 on rice solid cultures showed double peaks ofabsorption at 420 and 500 nm (Yongsmith et al. 2000).According to Domínguez-Espinosa and Webb (2003),pigments produced by M. purpureus Went (IMI-210765)on submerged fermentations with wheat flour-based

medium also presented two absorption peaks, although atslightly different wavelengths (400–410 and 490–500 nm).The addition of monosodium glutamate, soybean meal,peptone, or chitin powder to M. purpureus LPB 97 culturemedium containing jackfruit seed powder as substrateresulted in water-soluble pigments with maximum absorbancepeaks at 484 and 413, 482 and 405, 482 and 402, and 484 and385 nm, respectively, whereas single absorbance peakscorresponding to yellow pigment were obtained with thesupplementation of corn steep solid, malt extract, or yeastextract (Babitha et al. 2006). Therefore, the type of nutrientsin the medium, particularly nitrogen sources, significantlyinfluences the pattern of pigments produced (Miyake et al.2008). The water-soluble red pigments are nitrogen analogsof orange pigments, formed through reactions betweenthe latter and amino groups (Wong and Koehler 1983;Sabater-Vilar et al. 1999). In this sense, it is reported thatdifferent amino acids originate different pigment derivatives(Jung et al. 2003).

Studies involving Monascus spp. focuses mainly onconditions for pigment production (Pastrana et al. 1995;Fenice et al. 2000; Silveira et al. 2008). However, besidesthe growing food applications postulated for Monascuscolorants (Dufossé et al. 2005), relatively few studies dealwith the evaluation of pigment stability. In this sense,pigments produced by M. purpureus through submergedcultivations with SB (carbon source) and SPI (nitrogensource) as substrates were submitted to stability tests.

Selection of an adequate mathematical equation is animportant engineering tool to model an industrial processand brings an essential view to optimize processes, reduceintensity or time on industrial treatments, and minimize theimpact of processing on product quality. Therefore, fivekinetic equations that have been described to model thermaldegradation of food compounds were statistically evaluated.The results of fitting residual AU500/mL against the time ofthermal treatment to the kinetic models are shown inTable 2. Models that suggest the existence of a labile and aresistant fraction (Eqs. 4 and 5) were rejected by physicalcriteria. Rate parameters obtained by the statistical analysiswere negative, so these models cannot explain pigmentdegradation. The nth-order model was also rejected due tothe poorer fit of the experimental data when compared to

Fig. 2 Spectrum of M. purpureus extracellular pigments produced onsubmerged cultivations with sugarcane bagasse and soy proteinisolate. Aqueous solutions (pH 6.0) of Monascus pigments wereincubated at 80 °C for 0 h (A), 2 h (B), 4 h (C), or 6 h (D)

Table 2 Performance of selected models to describe the thermal degradation of M. purpureus red pigments

Model r2 χ2 SEM Remarks

First-order [0.802; 0.995] [4.0×10−5; 1.3×10−4] [1.1×10−5; 3.0×10−4] Higher r2 and lower χ2 and SEM; accepted

Weibull [0.752; 0.995] [7.4×10−5; 1.3×10−4] [1.3×10−4; 3.2×10−4] Low r2 and high χ2 and SEM; rejected

nth order [0.747; 0.994] [5.1×10−5; 1.3×10−4] [2.1×10−4; 4.6×10−4] Low r2 and high χ2 and SEM; rejected

Two-fraction [0.751; 0.996] [4.0×10−5; 10-4] [1.0×10−4; 9.2×10−4] Negative parameters estimates; rejected

Fractional conversion [0.756; 0.995] [7.4×10−5; 1.1×10−4] [1.0×10−4; 2.4×10−4] Negative parameters estimates; rejected

1010 Food Bioprocess Technol (2013) 6:1007–1014

other models (Table 2). Weibull distribution, which hasbeen proposed to describe heat inactivation of micro-organisms, enzymes, and pigments (Corradini and Peleg2004; van Boekel 2008), had good fit by analyzing thestatistical parameters. However, the first-order equationyielded the better adequacy of the experimental data,showing higher r2 values, in the range of 0.802 to 0.995,and lower χ2, from 1.3×10−4 to 4.0×10−5, and SEM,between 1.1×10−4 and 3.0×10−4. Moreover, for predictivemodeling, it is recommendable to choose the equation inwhich the fewest parameters are estimated because it ismore stable (due to the parameters being the leastcorrelated) to use the easiest model (Shockker and vanBoekel 1997). Thus, the first-order model seems to be thebest mathematical equation to describe the thermal degra-dation of the pigment produced by M. purpureus. Thisequation has been commonly used to describe heatdegradation of natural pigments, such as anthocyanins, invegetable juices (Reyes and Cisneros-Zevallos 2007;Harbourne et al. 2008; Kechinski et al. 2010).

The fit of experimental data to this model is graphicallyrepresented in Fig. 3. Kinetic parameters are summarizedin Table 3. The decimal reduction time (D value) is thetime needed for a tenfold reduction of the initial color at agiven temperature. It is obtained by plotting the residualcolor values on a log scale against the correspondinginactivation times. The z-value is the temperature needed

to reduce the D value by one log-unit, and it is obtained byplotting the D values on a log scale against thecorresponding temperatures. In heat processing, it iscommon to characterize first-order reactions in terms ofD and z values (thermal death time concepts). D values forheat degradation of Monascus pigment ranged from 357to 34 h in the temperature interval of 30–80 °C, and z-value was estimated to be 50 °C. Half-life times rangedfrom 107.5 to 10 h at 30–80 °C. Anthocyanins fromgrape, purple-flesh potato, red-flesh potato, and purplecarrot showed t1/2 of 15, 15, 34, and 33 h at 80 °C,respectively; D values of 2.1, 2.1, 4.7, and 4.5 days at80 °C; and z-values of 28, 28.4, 31.5, and 26 °C,respectively, in the 25–98 °C temperature range (Reyesand Cisneros-Zevallos 2007). The z-values for cookingand nutrient degradation (25–45 °C) are generally greaterthan that of, for instance, microbial inactivation (7–12 °C)(Awuah et al. 2007).

The logarithm representation of degradation ratesagainst the reciprocal temperature allows the calculationof activation energy (Ea), comparing the experimentaldata equation to the Arrhenius’ law. Arrhenius equation isgiven by Eq. 8.

k ¼ k0 expEa

RT

� �ð8Þ

where k0 is the Arrhenius constant, Ea the activationenergy, and R the universal gas constant (8.31 Jmol−1 K−1).

The k-values showed good fit to Arrhenius’ equation(Fig. 4); thus k0 and Ea were able to be calculated. Ea, theenergy barrier that molecules need to cross in order to react,is an important parameter for evaluating pigment stability(Liu et al. 2008). For Monascus pigments, the Ea wasobserved to be 40.8 kJ mol−1 (Table 4). The Ea fordegradation of blackberry anthocyanins in juice duringheating was 58.95 kJ mol−1 (Wang and Xu 2007), and thatfor blueberry anthocyanins was about 85 kJ mol−1 (Buckowet al. 2010). For betain and isobetain (red beet pigments),Ea values were 94.01 and 97.16 kJ mol−1, respectively (Liuet al. 2008).

The obtained value of k0 for M. purpureus pigment was1,141 min−1. It was possible to model the effect of bothvariables (time and temperature) on residual color by

Fig. 3 Degradation of M. purpureus pigments in aqueous solutions(pH 6.0) during heating at 30 (circles), 40 (squares), 60 (triangles),and 80 °C (diamonds) fitted to first-order model. The standard errorfor each point was less than 4%

Table 3 Kinetic parametersfor thermal degradationof M. purpureus red pigmentsat pH 6.0

aStandard error of regression(95% confidence interval)

Temperature (°C) k (E-3 min−1) t1/2 (h) D value (h) z-value (°C)

30 0.107±0.005a 107.52±4.81 357.16±16.07 50.12±2.2540 0.181±0.011 63.99±4.16 212.56±13.82

60 0.388±0.014 29.77±1.35 98.91±4.46

80 1.129±0.042 10.23±4.09 33.98±1.51

Food Bioprocess Technol (2013) 6:1007–1014 1011

substituting the Arrhenius equation into Eq. 1. Equation 9represents the combination of the first-order model andArrhenius equation.

A

A0¼ exp �1; 141 exp

�41; 000

8:31T

� �t

ð9Þ

where t is the time in minutes and T is the temperature inKelvin.

The time–temperature binomial is an essential issue tofocus in food industry, so the behavior of residual pigmentfollowing time–temperature treatments is shown in Fig. 5.A clear exponential behavior of pigment decay could beobserved with increasing the time and temperature treat-ments. The 3D representation is an interesting approachsince it offers the possibility to verify the interaction of timeand temperature on the residual pigment color. Redpigment discoloration at 30 and 40 °C is minimal, withonly 5% and 7% of pigment degradation after 6 h,respectively. At 60 °C, 86% of color maintenance wasobserved after 6 h and, at 80 °C, 32% of color was lost.These results demonstrate that Monascus pigments aresensitive to high temperatures (Wong and Koehler 1983;Fabre et al. 1993) and that color alterations should beexpected in thermally processed products containingMonascus pigments (Carvalho et al. 2005). Also, Fig. 2clearly shows the flattening of the absorbance peaks as the

incubation time progresses, illustrating the profile of colordecay at 80 °C and pH 6.0. Therefore, the results showthat Monascus pigments might tolerate pasteurizationconditions. However, more studies are necessary to verifythe interference of and/or interaction with food componentson pigment stability.

Studies on red pigments stability to pH values werecarried out at 80 °C, and pigment precipitation wasobserved at pH values of 4.0 and 5.0. Red pigmentsmaintained 81%, 84%, and 85% of the initial color after180 min at pH 6.0, 7.0, and 8.0, respectively. Afterautoclave treatment (121 °C for 15 min), pigment solutionsat pH 6.0, 7.0, and 8.0 showed 40%, 27%, and 20% ofcolor degradation. In both treatments (80 and 121 °C), therewas a trend of increased pigment stability at higher pHvalues. Fabre et al. (1993) reported greater sensitivity ofMonascus ruber red pigments at acidic pH, whereas higherstability was observed at neutral or alkaline conditions.Analogous results were obtained with pigments from M.purpureus N11S (Wong and Koehler 1983), which mayrepresent a problem for application of Monascus pigmentsin acidic foods, such as fermented milks. The resultsindicate that Monascus pigments may possibly be used as

Fig. 4 Arrhenius representation of constants of M. purpureus pigmentdecolorization during heating. The regression equation was determinedas y=4910.8x−7.04 (r2=0.990)

Table 4 Thermodynamicparameter values forM. purpureus red pigmentdecay at pH 6.0

Temperature (K) Ea (kJ mol−1) ΔH# (kJ mol−1) ΔG# (kJ mol−1) ΔS# (J mol−1 K−1)

303 40.81±1.64 38.29±1.54 86.91±3.48 −160.47±8.32313 38.21±1.51 88.52±3.52 −160.73±8.36333 38.04±1.47 92.23±3.37 −162.72±8.24353 37.88±1.55 94.80±3.41 −161.27±8.28

Fig. 5 Residual color of M. purpureus red pigment as a function oftime and temperature at pH 6.0. Mathematical model (Eq. 9) was acombination of first-order and Arrhenius equations

1012 Food Bioprocess Technol (2013) 6:1007–1014

colorants in foods having neutral or slightly acidic orbasic pH values (6.0–8.0) and in production processesinvolving only moderate thermal treatments, preferablylower than 60 °C. The color degradation observed in thisstudy is a common characteristic of natural pigments,which is usually compensated by proper pigment dosage(Carvalho et al. 2005).

Estimation of thermodynamic parameters may providevaluable information concerning the kinetics of pigmentthermal degradation and structure-stability modifications.The good fit of pigment degradation rates to the Arrheniusequation (Fig. 4) enabled the calculation of activationenthalpy (ΔH#), free energy of inactivation (ΔG#), andactivation entropy (ΔS#) for pigment degradation (Table 4)as described elsewhere (Lappe et al. 2009). ΔH# and ΔS#

values for heat degradation provide a measure of thenumber of non-covalent bonds broken and of the disorderchange of the system, respectively. Values of ΔH# and ΔG#

decreased and increased, respectively, as the temperaturewas raised. The ΔH# values indicate that conformationalterations have occurred (Bhatti et al. 2006), and from theΔG# values, it is suggested that reaction conditions fordegradation were not favored at higher temperatures from athermodynamic point of view (Basu et al. 2008), whichcould be due to the negative entropic contribution to thedegradation process. In fact, the negative ΔS# values fordegradation indicate that this system presents a low level ofdisorderliness (Bhatti et al. 2006).

In conclusion, this work described the production of M.purpureus NRRL 1992 red pigments with SB as carbonsource. The utilization of SB, an abundant agro-industrialresidue, may represent an added value to the industry andan environment-friendly manner for waste management.Red pigments presented moderate stability when exposed toconditions of acidic pH and/or high temperatures. Thermaldegradation of red pigments produced by Monascus (withSB and SPI as substrates) was shown to be best representedby first-order kinetics. Pigment stability is a fundamentaltechnological issue, and color decay modeling is ofimportance for food processors intending to apply Monascuspigments as food colorants.

Acknowledgments A. Brandelli is a research fellow of CNPq, Brazil.

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