Nonfat Yogurt Research Articles

Effect of transglutaminase on proteolysis and rheological properties of nonfat yoghurt

در این تحقیق، تاثیر غلظت آنزیم ترانس گلوتامیناز میکروبی، میزان کازئینات سدیم و زمان نگهداری بر پروتئولیز، خواص رئولوژیکی و ظرفیت نگهداری آب در ماست همزده بدون چربی با استفاده از روش سطح پاسخ مورد بررسی قرار گرفت. غلظت آنزیم در محدوده 2-0 واحد در گرم پروتئین شیر، میزان کازئینات سدیم در دامنه 27/1-0 درصد و زمان نگهداری بین 19-1 روز بود. نتایج تجزیه آماری داده ها نشان داد که با افزایش غلظت آنزیم ویسکوزیته و ظرفیت نگهداری آب در نمونه ها به طور معنی داری افزایش و میزان پروتئولیز در آنها کاهش یافت (p≤0.05). با افزودن کازئینات سدیم نیز ویسکوزیته، ظرفیت نگهداری آب نمونه ها افزایش پیدا کرد. همچنین در طی نگهداری، ظرفیت نگهداری آب کاهش و میزان پروتئولیز افزایش معنی داری نشان داد (p≤0.05). در شرایط بهینه، غلظت آنزیم 42/1 واحد در گرم پروتئین شیر، میزان کازئینات سدیم 47/0 درصد و زمان نگهداری 15 روز تعیین گردید. مقدار مطلوبیت کلی برابر 83/0 بود. در شرایط مزبور درصد ظرفیت نگهداری آب، ویسکوزیته و پروتئولیز به ترتیب 51/27 درصد، 5220 سانتی پوآز و میزان جذب آن در طول موج 340 نانومتر به عنوان شاخص پروتئولیز 349/0 بود.

Amylose–Potassium Oleate Inclusion Complex in Plain Set‐Style Yogurt

Health and wellness aspirations of U.S. consumers continue to drive the demand for lower fat from inherently beneficial foods such as yogurt. Removing fat from yogurt negatively affects the gel strength, texture, syneresis, and storage of yogurt. Amylose-potassium oleate inclusion complexes (AIC) were used to replace skim milk solids to improve the quality of nonfat yogurt. The effect of AIC on fermentation of yogurt mix and strength of yogurt gel was studied and compared to full-fat samples. Texture, storage modulus, and syneresis of yogurt were observed over 4 weeks of storage at 4 °C. Yogurt mixes having the skim milk solids partially replaced by AIC fermented at a similar rate as yogurt samples with no milk solids replaced and full-fat milk. Initial viscosity was higher for yogurt mixes with AIC. The presence of 3% AIC strengthened the yogurt gel as indicated by texture and rheology measurements. Yogurt samples with 3% AIC maintained the gel strength during storage and resulted in low syneresis after storage for 4 wk.

The role of Yogurt in improving the quality of the American diet and meeting dietary guidelines

The Dietary Guidelines for Americans (DGA) recommend three daily servings of low- or nonfat dairy products, yet two-thirds of individuals in the United States do not meet that goal. Including low- or nonfat yogurt as part of an overall healthful diet can be a positive step toward meeting the DGA recommendations. Yogurt naturally contains calcium and potassium, and some products are fortified with vitamin D. All of these nutrients were identified in the DGA as "nutrients of concern," because typical intake falls far short of recommended intakes. Yogurt can also be an excellent source of high-quality protein, which promotes satiety, helps in maintaining a healthy body weight, and aids muscle and bone growth. In addition, yogurt is low in sodium and contributes 1.0% or less of added sugars to the diets of most individuals in the United States; however, 90% of children and adults consume less than 8 ounces (1 cup) of yogurt per week. Thus, consuming 1 serving of yogurt per day would help to meet the DGA-recommended dairy servings and would provide nutrients of concern.

Effect of Transglutaminase on Texture and Flow Properties of Stirred Probiotic Yoghurt during Storage

AbstractThe aim of this work was to study the effect of different concentrations of transglutaminase (TG), inactivated or not inactivated – 0.02, 0.06 and 0.12% (w/w) – on the textural characteristics and flow properties of stirred probiotic yoghurt prepared from pasteurized skim milk (0.1% [w/w] fat). The physicochemical characteristics and the textural and rheological properties of yoghurt samples were determined after production and during 10 days of storage. The gel structure of yoghurt samples produced with not inactivated TG was stronger than that of samples produced with inactivated TG and control sample. Yoghurt containing 0.12% (w/w) TG not inactivated showed the highest hysteresis loop area (3,580 Pa·s) after 5 days of storage. Hysteresis loop area of samples with 0.12% (w/w) inactivated TG after incubation for 2 h at 40C is 56% lower compared with samples manufactured with the same concentration of not inactivated TG after 10 days of storage.Practical ApplicationsTo produce yoghurt with low energy value, improved gel characteristics, and good physical and chemical properties, enzyme transglutaminase (TG) can be used. Enzymes are potential tools to increase the formation of covalent cross‐links in protein foods. The addition of TG can reduce proteins and milk fat to produce nonfat yoghurt with the same rheological characteristic as yoghurt from whole fat milk. There are two different ways for the application of TG: simultaneously or prior to the fermentation. In the first case, TG was simultaneously added with starter culture. Pretreatment of milk with TG addition prior to fermentation demands additional process time as well as thermal inactivation step and has the advantage of a constant pH during the cross‐linking reaction.

Increased Dairy Consumption Differentially Improves Metabolic Syndrome Markers in Male and Female Adults

Effects of dairy consumption on metabolic health and adiposity are inconsistent. Most clinical trials have investigated dairy intake, frequently during caloric restriction, in overweight or obese populations but not in a metabolic syndrome population. We investigated the effect of increased dairy intake without caloric restriction on anthropometrics, plasma lipids, and glucose in typically low-dairy consumers who met the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) metabolic syndrome criteria. Male (n=14) and female (n=23) adults (54.1 ± 9.7 years) with metabolic syndrome were randomized to consume low-fat dairy (LFD) (10 oz of 1% milk, 6 oz of nonfat yogurt, 4 oz of 2% cheese) or carbohydrate control (CNT) (1.5-oz granola bar and 12 oz of 100% juice) foods for 6 weeks in a crossover study design. Anthropometrics, metabolic syndrome parameters, insulin resistance, and parathyroid hormone were measured. Body composition was analyzed by a dual-energy X-ray absorptiometry scan for a subset of subjects (n=22). LFD modulated metabolic syndrome parameters differently according to gender. Following LFD, men had lower glucose (95.4 ± 9.1 vs. 98.9 ± 10.6 mg/dL, P=0.048), whereas women had lower body weight (BW), waist circumference, and body mass index (P<0.01) compared to CNT. Women also had lower energy intake following LFD compared to CNT. Increases in phosphorus (a dairy nutrient) were negatively correlated with decreases in BW (r=-0.537; P<0.01) and body fat in women (r=-0.593, P<0.025), whereas the decreases in energy intake had no correlation with anthropometrics. Three dairy servings/day promoted small but significant improvements differentially by gender in a metabolic syndrome population.

Sensory properties and drivers of liking for Greek yogurts

Greek yogurt is currently the largest growing sector in the dairy industry. Because no standard of identity exists for Greek yogurts in the United States, and they can be made by a variety of methods, variability in sensory properties is expected. Knowledge of consumer perception and specific drivers of liking will be useful information for product developers. The objective of this study was to document the sensory properties of commercial Greek yogurts and to determine drivers of liking through descriptive profiling and consumer testing. Flavor and texture attributes of commercial Greek yogurts (n=24) were evaluated in triplicate by a trained descriptive sensory panel. An online survey (n=520) was used to collect consumer usage and attitude information for Greek yogurts before consumer acceptance testing. Consumer acceptance testing (n=155) was then conducted on commercial Greek yogurts (n=10). Univariate and multivariate statistical analyses were used for data analysis. Sensory properties of yogurt differed with fat content and manufacture (Greek vs. fortified Greek). Full-fat yogurts were characterized by firmness and denseness, whereas low- and non-fat yogurts lacked firmness, denseness, cohesiveness, and, after stirring, viscosity. Fortified Greek yogurts generally had more surface shine and jiggle and lower denseness compared with traditional Greek yogurts. Fewer flavor differences were observed among yogurts compared with texture differences. Fortified Greek yogurts displayed a burnt/beefy flavor not documented in traditional Greek yogurts, but this flavor was not evident in all fortified Greek yogurts. Consumer preferred Greek yogurts with firm, dense texture, moderate sweet aromatic, milkfat and dairy sour flavors, and moderate sour taste. Consumers were aware of the increased protein content of Greek yogurts but generally unaware of differences between strained and fortified Greek yogurts; both strained Greek and fortified Greek yogurts received the highest overall liking scores in blinded acceptance testing. Successful Greek yogurts can be manufactured using addition of dried dairy ingredients or by traditional straining and centrifugation.

Characterization of recombinant Zea mays transglutaminase expressed in Pichia pastoris and its impact on full and non‐fat yoghurts

Transglutaminases catalyze post-translational modification of proteins by ε-(γ-glutamyl) links and covalent amide bonds. Research on properties and applications of plant transglutaminases is less developed than in animals and micro-organisms. In a previous study, optimized Zea mays transglutaminase was purified from recombinant Pichia pastoris strain. The main objective of the present study was to characterize this enzyme and assess its effect on the properties of yoghurt. The purified recombinant transglutaminase presented a Km of 3.98 µmol L(-1) and a Vmax of 2711 min(-1) by the fluorometric method. The enzyme was stable after incubation for 30 min below 50 °C and over a broad pH range of 5-8 at -20 °C for 12 h. The results showed that the crosslinking reaction catalyzed by this enzyme could effectively improve the properties of full and non-fat yoghurts. Also, the properties of non-fat yoghurt could be improved similar to the full-fat product by recombinant transglutaminase. The application of recombinant transglutaminase in yoghurt indicated that this enzyme could be used as a substitute for microbial transglutaminase in the production of yoghurt, thus providing experimental evidence for the future application of plant transglutaminases in the food industry.

Fortification of yoghurts with grape (Vitis vinifera) seed extracts

The feasibility of full-fat and non-fat yoghurts fortification with grape seed extracts from two grape varieties, namely Moschofilero and Agiorgitiko, was examined. Epicatechin, total phenolics, antiradical activity, reducing power, viable Lactobacilli counts and pH of fortified and not fortified yoghurts were followed throughout products' shelf life. The fortification of yoghurts at 5–10 mg gallic acid equivalents/100 g of yoghurt did not affect yoghurt pH and Lactobacilli counts and – as perceived by the authors during tasting – did not cause major defects in consistency, colour and flavour compared to controls; differences in colour were detectable by colorimetry. Seed polyphenols were detected in supplemented yoghurts, in amounts proportional to those of seed extracts. Fortified yoghurts contained more polyphenols and exhibited higher antiradical and antioxidant activity than controls, even after 3–4 weeks of cold storage. The degradation of polyphenols and the decrement of yoghurts' antiradical and antioxidant activities followed first order kinetics, with full-fat yoghurts exhibiting higher deterioration rates and lower half-lives than the non-fat ones. It is concluded that, at the supplementation levels tested, the production of functional yogurts with grape-seed antioxidants is feasible, given that the supplementation is carried out in the fermented product and not in milk prior to fermentation.

Effect of microfluidization of heat-treated milk on rheology and sensory properties of reduced fat yoghurt

The effects of microfluidization at 150 MPa (MFz) and conventional homogenization at 20/5 MPa (CH) of heat-treated milk on the rheology and sensory properties of non- (0.1%) and low- (1.5%) fat stirred yoghurts were compared. Homogenization conditions clearly affected the sensory properties of reduced-fat yoghurts, but the effect was highly dependent on fat content. MFz of heat-treated milk yielded products with very different sensory profiles from the conventional yoghurts. For non-fat yoghurts, MFz of heat-treated milk enhanced the perception of buttermilk and soft cheese flavours, and natural yoghurt aroma and flavour, but also increased the intensity of undesirable mouthfeel characteristics such as chalkiness, mouth-dryness and astringency. For low-fat yoghurts, MFz significantly improved creaminess and desirable texture characteristics such as smoothness, cohesiveness, thickness, and oral and spoon viscosity. These differences in sensory profiles, especially textural properties, were partially related to rheological properties, particularly flow behaviour. MFz of heat-treated milk resulted in non- and low-fat yoghurts with higher yield stress, more pronounced hysteresis effect and higher viscosity than those of CH yoghurts of similar fat contents. These findings suggest that microfluidization may have applications for production of high-quality yoghurt with reduced-fat content.

Effect of oxidoreduction potential on aroma biosynthesis by lactic acid bacteria in nonfat yogurt

The aim of this study was to investigate the effect of oxidoreduction potential (Eh) on the biosynthesis of aroma compounds by lactic acid bacteria in non-fat yogurt. The study was done with yogurts fermented by Lactobacillus bulgaricus and Streptococcus thermophilus. The Eh was modified by the application of different gaseous conditions (air, nitrogen, and nitrogen/hydrogen). Acetaldehyde, dimethyl sulfide, diacetyl, and pentane-2,3-dione, as the major endogenous odorant compounds of yogurt, were chosen as tracers for the biosynthesis of aroma compounds by lactic acid bacteria. Oxidative conditions favored the production of acetaldehyde, dimethyl sulfide, and diketones (diacetyl and pentane-2,3-dione). The Eh of the medium influences aroma production in yogurt by modifying the metabolic pathways of Lb. bulgaricus and Strep. thermophilus. The use of Eh as a control parameter during yogurt production could permit the control of aroma formation.

Application of Renneted Skim Milk as a Fat Mimetics in Nonfat Yoghurt

For a long time, fermented dairy products have been consumed for human’s nutrition and health. Recently, consumption of whole dairy products, such as full fat yoghurt, has declined due to the awareness of probable harmful effects of fat on consumers’ health, resulting change of market interest in favor of low or non fat dairy products. It is a challenge for food scientists to produce a suitable fat substitute providing the functionality of the missing fat. The present investigation was carried out to examine the effect of 0 to 50% renneted skim milk (RSM) as a fat mimetic upon the physico-chemical, physical, rheological and sensory characteristics of nonfat yoghurt in comparison to control samples (full fat and skim yoghurt). By increasing RSM content, the chemical characteristics (titratable acidity, pH as well as the content of fat and total protein) of yoghurts did not alter except decrease of total solid in sample with 50% RSM. The yoghurts with more content of RSM exhibited higher b*and a* values, while the highest L* value, viscosity, water holding capacity (WHC), firmness and lowest syneresis were found in sample containing 30% RSM. It seems that new interaction in gel network of yoghurts containing RSM, exhibited greater ability to bind water than control skim yoghurt. In addition, probably new bridges between milk proteins (interacting partially hydrolyzed casein with casein) can increase the number of bounds between protein particles leading to lower syneresis. However, excessive RSM content (higher than 30%) did not increase the L* value, viscosity and WHC of samples probably because of too much aggregation of casein. Sensory results revealed that sample containing 30% RSM was exactly alike to full fat yoghurt in terms of overall sensory attributes. New formulation of palatable skim yoghurt was developed using 3% RSM successfully.

Impact of a plant extract on the viability of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus in nonfat yogurt

The effect of a plant extract (prepared from olive, garlic, onion and citrus with sodium acetate as a carrier) on the viability of yogurt starter cultures was studied. Nonfat yogurt was prepared with various levels of supplements: plant extract (0, 0.5 or 1.0%, w/v) or l-cysteine HCl (0.014 or 0.028%, w/w). Microbial and physicochemical analyses were conducted weekly for 50 days. Fermentation time increased for supplemented yogurts compared with the non-supplemented yogurt. Lactobacillus bulgaricus counts in supplemented yogurts were >6 log cfu mL −1 for a longer time (7–21 days) compared with the non-supplemented yogurt. Streptococcus thermophilus counts in all yogurts were > 6 log cfu mL −1 throughout the storage. Overall, redox potential and titratable acidity of yogurts on day 50 were greater compared with day 1, but pH and syneresis were less. Plant extract at 0.5% enhanced L. bulgaricus viability in nonfat yogurt while least affecting the physicochemical characteristics.

The influence of transglutaminase treatment on functional properties of set yoghurt

The objective of this study was to investigate the effect of transglutaminase (Tgase) on the functional properties of set yoghurt, due to enzymatic cross‐linking of the milk proteins. Yoghurt samples were prepared from three formulations: reconstituted skim milk, and whole milk containing two different solid‐non‐fat (SNF) content, with four enzyme treatments: Control (no enzyme) and three microbial Tgase treatments: Pre‐incubated 90 min, Pre‐incubated and inactivated after 90 min, Not pre‐incubated. The modifications which were caused by Tgase were found to be more clear when Tgase was active in set type yoghurts. It was found that nonfat yoghurt sample with lower SNF content can be produced with improved textural properties using Tgase.

Impact of oxidoreduction potential and of gas bubbling on rheological properties of non-fat yoghurt

The aim of this work was to study the effect of different gaseous conditions on the physico-chemical properties of yoghurt. Four conditions of oxidoreduction potential (Eh7), +433 mV (milk gassed with air), +405 mV (ungassed milk), +283 mV (milk gassed with N2) and −349 mV (milk gassed with N2–H2) were applied to milk. The rheological properties and microstructure of these yoghurts were determined by measuring apparent viscosity, whey separation (WS) and using confocal laser scanning microscopy. Exopolysaccharide (EPS) production by lactic acid bacteria (LAB) was also studied, and production was increased for extreme Eh7 values: the highest values were obtained for air (oxidizing condition) and for N2–H2 (reducing condition). Yoghurts made under bubbled N2–H2 clearly led to low WS with higher gel aggregation and a lower proportion of pores.

Texture of nonfat yoghurt as influenced by whey protein concentrate and Gum Tragacanth as fat replacers

Seven batches of nonfat yoghurt stabilized with different concentrations of whey protein concentrate (WPC) and Gum Tragacanth (GT) were produced to study the effects of WPC and GT as fat replacers on the rheological properties of yoghurt. By increasing the WPC up to 15 g/L, storage modulus (G′), loss modulus (G″) and complex dynamic viscosity (η*) values were increased and sensory impressions of texture and appearance were improved when compared with the control nonfat yoghurt. Addition of gum above 0.5 g/L led the decrease of G′, G″, η* and resulted in lower scores for sensory attributes than control nonfat yoghurt.

Probiotic stability of yoghurts containing Jerusalem artichoke inulins during refrigerated storage

Experimentally prepared Jerusalem artichoke inulins (JAI) were compared with two commercial chicory root inulins for their prebiotic potentials in media broth model and growth-sustaining ability in non-fat yoghurts. Experimental yoghurts were made with 12% reconstituted skim milk (RSM) supplemented with 4% inulin powders, inoculated with mixed cultures of Lactobacillus casei LC-01, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (1:0.5:0.5 based on supplier’s recommendation) and incubated overnight at 37 °C. Non-supplemented yoghurt was prepared from 16% RSM and used as control. The survival and acidifying activity of lactic and probiotic cultures in all yoghurts were investigated on weekly intervals during the shelf life of 28 days at 4 °C. Incorporation of JAI resulted in improved viability of LC-01, maintaining >7.0 log CFU/g during cold storage but did not affect the viability of yoghurt bacteria in comparison with the control.

RHEOLOGY AND TEXTURE OF SET YOGURT AS AFFECTED BY INULIN ADDITION

ABSTRACT The effect of inulin addition on rheology and texture of nonfat yogurt (NFY) was studied by the large (texture analyzer) and small (dynamic oscillatory rheometry) deformation tests. Skim milks (12% solids) were supplemented with three commercial chicory inulins with different chain lengths at 4% level and inoculated with mixed cultures of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus. Textural and rheological tests were conducted after an overnight storage at 4C and during a shelf life of 28 days. A good correlation was observed between the two tests. During storage, all inulin‐containing yogurts in comparison with the control NFY were characterized by lower values of firmness, apparent viscosity, yield stress, complex viscosity, storage modulus and loss modulus. NFYs supplemented with long‐chain inulin demonstrated a rheological behavior closer to that of control full‐fat yogurt.PRACTICAL APPLICATIONSThe use of inulin and oligofructose in the food industry has grown recently because of their interesting nutritional and technological properties. In the work presented here, three commercial inulin products with different chemical composition and functions were added to yogurt milk, and changes in rheological properties of yogurt were investigated in comparison with nonsupplemented control yogurts. According to the manufacturer's specifications, Raftiline HP and Raftiline GR are suitable for fat replacement because of the presence of long‐chain inulins, while Raftilose P95, being rich in mono‐ and disaccharides, is highly recommended for sugar replacement. The knowledge obtained from this study may be applied for the development of nonfat yogurts to satisfy the nutritional expectations of ever‐increasing health conscious consumers and at the same time to match the sensory and textural characteristics of full‐fat yogurt.

Whey Protein Concentrate and Gum Tragacanth as Fat Replacers in Nonfat Yogurt: Chemical, Physical, and Microstructural Properties

The effect of whey protein concentrate (WPC) and gum tragacanth (GT) as fat replacers on the chemical, physical, and microstructural properties of nonfat yogurt was investigated. The WPC (7.5, 15, and 20g/L) and GT (0.25, 0.5, 0.75, and 1g/L) were incorporated into the skim milk slowly at 40 to 45°C with agitation. The yogurt mixes were pasteurized at 90°C for 10min, inoculated with 0.1% starter culture, and incubated at 42°C to pH 4.6, then refrigerated overnight at 5°C. A control nonfat yogurt and control full fat yogurt were prepared as described, but without addition of WPC and GT. Increasing amount of WPC led to the increase in total solids, total protein, acidity, and ash content, whereas GT did not affect chemical parameters. Increasing WPC caused a more compact structure consisting of robust casein particles and large aggregates. Firmness was increased and susceptibility to syneresis was decreased as WPC increased. No significant difference was observed for firmness and syneresis of yogurt fortified with GT up to 0.5g/L compared with control nonfat yogurt. Increasing the amount of gum above 0.5g/L produced softer gels with a greater tendency for syneresis than the ones prepared without it. Addition of GT led to the coarser and more open structure compared with control yogurt.

EFFECTS OF FUNCTIONAL DAIRY BASED PROTEINS ON NONFAT YOGURT QUALITY

ABSTRACT Production of nonfat yogurt demands a careful control of quality parameters. It is common to use skim milk powder (SMP) to increase the total solid content of nonfat yogurt, but some functional dairy‐based proteins, such as casein/caseinates and whey proteins, may improve the quality of nonfat yogurt. The objectives of this study were to use whey protein isolate (WPI), sodium caseinate (NaCn) and yogurt texture improver (TI) in nonfat yogurt manufacture as an alternative for SMP, and to compare their potential influences on the physical, chemical and microbial properties of nonfat yogurts over a 12‐day storage. All dry ingredients were added at 1% (w/v) concentration to yogurt milk. Yogurts differed from each other with different hardness values. Acetaldehyde contents of yogurts were in the range of 35–43 ppm. The acetaldehyde content of all yogurt types decreased during storage. The control yogurt had the most tyrosine content, and the WPI‐fortified yogurt had the least. Using different dry dairy ingredients did not affect the numbers of starter cultures. In addition, no significant differences were observed among yogurt types regarding their mineral composition. PRACTICAL APPLICATIONSFunctional dry dairy ingredients can be used to increase the total solid content of nonfat yogurt instead of using skim milk powder (SMP) or evaporation. Their high protein content, water‐binding capacity, texture improvement properties and health benefits make these proteins suited for use in nonfat yogurts. This study compares the possible effects of using whey protein isolate (WPI), sodium caseinate (NaCn) and yogurt texture improver (TI) as an alternative for SMP on the physical, chemical and microbial properties of nonfat yogurts. It was found that substitution of SMP for WPI, NaCn and TI at the level of 1% affected the physical, chemical and microbial properties of nonfat yogurt.

The influence of additives on the rheological and sensory properties of nonfat yogurt

In this work, response surface methodology was applied to a study of the effects of the addition of skim milk powder and stabilizers on the apparent viscosity and sensory attributes of nonfat yogurt. The addition of stabilizers has been shown to produce a significant effect on sensory attributes, while high concentrations of xanthan and guar gum are seen to decrease the overall acceptability of the yogurt, with gelatin producing the higher apparent viscosity and consistency. The correlation among apparent viscosity, which is an instrumental measurement, and consistency, which is a sensory evaluation, was 0.72.