Hossein Jooyandeh; Erfan Danesh; Mostafa Goudarzi
Abstract
Introduction: Health-conscious consumers are interested in eating dairy products including ice cream with less fat. As a consequence, the dairy industry has developed a variety of reduced-fat ice cream products. However, quality aspects of many of these products do not meet consumer expectations for ...
Read More
Introduction: Health-conscious consumers are interested in eating dairy products including ice cream with less fat. As a consequence, the dairy industry has developed a variety of reduced-fat ice cream products. However, quality aspects of many of these products do not meet consumer expectations for ice cream flavor, texture, and appearance. The formation of the ice cream structure is hindered when the fat content is reduced and attributes related to quality, such as viscosity, ice crystallization, hardness, melting rate and flavor, are affected. Low melting resistance, high firmness and undesirable flavor are the most cited defects in reduced-fat ice creams. Enzymatic treatment of reduced-fat milk with microbial transglutaminase has been found to improve the textural and sensory properties of the final dairy products. The transglutaminase enzyme (MTGase; protein-glutamine gamma glutamyl transferase, EC 2.3.2.13) catalyses “acyl” transfer reactions between γ-carboxyamide groups of glutamine residues (acyl donor) and the ɛ-amino group of lysines (acyl acceptor) in proteins, leading to inter- or intra-molecular cross-linking. The enzyme-catalyzed cross-linking of milk proteins results in the formation of high molecular weight polymers that not only are able to lower the melting rate thorough increasing the viscosity of ice cream mix, but they could also provide a smoother texture for the product by mechanically obstructing ice crystal growth. However, the extensive cross-linking of milk proteins may even adversely affect the physical properties of the resultant ice cream and thus, the added amount of enzyme needs to be adequate for the desired effects. The aim of this study was to investigate the effects of different concentrations of TGase enzyme on physical and sensory properties of light ice cream in order to selct the appropriate amount of enzyme concentration that provides the best results.
Materials and methods: The light ice cream (5% w/w fat) was treated with different concentrations of TGase enzyme (2, 4 and 6 units/g milk protein). The enzyme-treated samples were investigated for flow behavior characteristics (apparent viscosity, flow index, consistency index), overrun, melting rate, hardness and sensory properties (flavor, texture, color and total acceptability) in comparison with control light ice cream with no added Tgase.
Results and discussion: The results revealed that TGase treatment effectively increased the viscosity of light ice cream.The higher the enzyme concentration, the greater the viscosity of ice cream samples. This could be attributed to TGase-catalyzed formation of large protein polymers in ice cream mix that resist to flow. All enzyme-treated ice cream mixes exhibited shear-thinning behavior, where the viscosity decreased with increasing shear rate. The power law model was used to find consistency and flow indices for different treatments. The results showed that consistency index increased and flow behavior index decreased with TGase concentration. The stronger shear-thinning behavior (lower flow index) of the samples treated with higher concentration of TGase might be arisen from formation of higher number of large protein polymers in theses samples, which decrease in size during shearing. The enzyme treatment significantly increased the overrun of the light ice cream that could be due to the increasing effect of TGaes on the viscosity. The increase in viscosity promotes the retention of air in the ice cream which is concomitant with increased overrun; however, high viscosity reduces the whipping rate leading to lower incorporation of air into the ice cream and thus decreased overrun. This may account for significantly lower overrun of the light ice cream treated with 6 units TGase/g milk protein than the samples treated with 4 units TGase /g milk protein. It was observed that the enzyme treatment caused a significant improvement in melting resistance of light ice cream. In fact, the light ice cream treated with 6 or 4 units TGase /g milk protein took the longest time to melt, followed by the samples treated with 2 and 0 units TGase /g milk protein. This is somehow in accordance with the results of overrun; that is, the ice cream with higher overrun melted slower attributed to a reduced rate of heat transfer due to a larger volume of air. The overrun could also affect the hardness of ice cream as evidenced by the results of the present study. The results showed that the samples with greater overrun were softer. It could be assumed that the air cells, together with large protein polymers formed via catalytic action of TGase, limited the size of ice crystals by exerting mechanical hindrance, providing a softer texture for the enzyme-treated ice creams. Not surprisingly, the enzyme treatment did not considerably influence the flavor of light ice cream albeit the sample treated with 6 units TGase /g milk protein received significantly lower score than the other samples. Conversely, the color of enzyme-treated samples was more appreciated by consumers than the sample without added TGase possibly because of light scattering properties of enzymatically formed protein polymers in theses samples. Consistent with the results of physical properties, the texture of light ice cream treated with 4 or 6 units TGase /g milk protein were ranked as the most desirable samples, followed by the samples treated with 2 and 0 units TGase /g milk protein. The order of light ice cream samples for total acceptability scores was the same as that for texture scores with the exception of the sample treated with 6 units TGase /g milk protein whose total acceptability score was lower than the sample treated with 4 units TGase /g milk protein.
Erfan Danesh; Hossein Jooyandeh; Vahid Samavati; Mostafa Goudarzi
Abstract
Introduction: Scientific evidence has demonstrated that consumption of high-fat foods has direct connection with increasing incidences of various diseases such as obesity, diabetes, hardening of the artery walls and blood pressure. Thus, demand for low-fat foods has increasingly been promoted by health-conscious ...
Read More
Introduction: Scientific evidence has demonstrated that consumption of high-fat foods has direct connection with increasing incidences of various diseases such as obesity, diabetes, hardening of the artery walls and blood pressure. Thus, demand for low-fat foods has increasingly been promoted by health-conscious consumers. However, development of low-fat foods is challenging as fat makes a major contribution to sensory attributes of many foods. Low-fat cheeses are usually characterized as having a flat taste, more translucency and a rubbery and gummy texture. A common strategy for improving the properties of low-fat cheeses is to increase its moisture content sufficiently to provide moisture to protein ratio which is greater than or equal to its full-fat counterpart. The addition of denatured whey proteins, which are known for their high water-holding capacity, to cheese milk is one method used to achieve this objective. Likewise, transglutaminase treatment of cheeses milk has been shown to increase the moisture content of the resultant cheese. Enzyme transglutaminase (MTGase; protein-glutamine gamma glutamyl transferase, EC 2.3.2.13) catalyzes acyl transfer reactions between protein intra- or inter- chain glutamine (acyl donor) and lysine (acyl acceptor) peptide residues. UF-Feta cheese has the highest per capita consumption amongst cheese varieties in Iran. However, UF-Feta cheese is also perceived as being high in fat, discouraging some consumers from including it in their diets. The objective of this study was enzymatic incorporation of whey proteins into the formulation of UF-Feta cheese by TGase in order to obtain a low-fat product with desirable textural and sensory properties.
Materials and methods: The experiments were designed according to a 5-level-3-factor central composite design using response surface methodology (RSM). The independent variable were formulation ingredients including TGase enzyme (0-2 units/g protein), whey protein concentrate (WPC) (0-16 % w/w) and fat (0-10 % w/w) and the responses of interest were the physicochemical (moisture content and lightness (L*)), textural (hardness, adhesiveness, cohesiveness and springiness) and sensory properties (flavor and odor, color and appearance, texture and total acceptability) of UF-Feta cheese.
Results and discussion: The results indicated that fat reduction caused significant increment in the moisture content of UF-Feta cheese. The whey protein addition showed the same effect on moisture content as fat reduction whereas transglutaminase treatment decreased the moisture of UF-Feta cheese. As expected, fat reduction was accompanied by an increase in hardness and elasticity of UF-Feta cheese. Fat and moisture act as fillers in the casein matrix of cheese texture. When the fat content is decreased, the moisture does not replace the fat on an equal basis, so the total filler volume is decreased, resulting in lower moisture to protein ratio. This in turn increases possibilities of cross-linking between protein chains, resulting in a more compact cheese matrix with harder and chewier texture. Similarly, the increasing effect of TGase treatment on hardness and elasticity may be attributed to formation of a more compact protein matrix because of cross-linking action of enzyme on milk proteins. The whey proteins, however, decreased the hardness and elasticity of UF-Feta cheese. It seems that the added whey proteins increased the moisture content of cheese as sufficiently as to offset the decrease in the total filler volume caused by fat reduction, preventing the protein matrix to be more compact and elastic. Promoted protein-protein interactions of the cheese matrix resulting from fat reduction or TGase treatment might also account for our observation on decreased adhesiveness and increased cohesiveness. As the protein matrix becomes more compact, the cheese loses its adhesiveness. Conversely, as the number or strength of protein interactions increases, the structural integrity of cheese matrix called cohesiveness increases. Apart from fat, water can also create more open conformation for protein molecules, resulting in increased adhesiveness and decreased cohesiveness. This may justify our observation on higher adhesiveness and lower cohesiveness of whey protein-fortified low-fat cheeses with high moisture content. Not surprisingly, all the sensory attributes of UF-Feta cheese were adversely influenced by fat reduction. On the other hand, whey proteins improved the flavor and texture of low-fat UF-Feta cheeses. They, however, showed no effect on appearance score of cheese samples in spite of the fact that they somewhat compensated for lost lightness (L*) of low-fat cheeses. Similarly, TGase treatment did not affect the appearance acceptability of UF-Feta cheeses despite having significant effect on their L* value. The sensory panel did not appreciate the flavor of TGase-treated samples; however, they scored the samples treated with enzyme concentration lower than 1 U/g protein as having desirable texture. RSM suggested that the optimum formulation of 5.95% (w/w) fat, 0.56 unit TGase per gram protein and 8.79% (w/w) WPC could produce a low-fat cheese sample with desired textural (hardness 0.342 kg; elasticity 8.58 mm; adhesiveness -0.070 kg.s; cohesiveness 0.474) and sensory (overall sensory score 88.73 out of 100) attributes.
