Yogurt Flavor Research Articles

Genome-Scale Model of Streptococcus thermophilus LMG18311 for Metabolic Comparison of Lactic Acid Bacteria

In this report, we describe the amino acid metabolism and amino acid dependency of the dairy bacterium Streptococcus thermophilus LMG18311 and compare them with those of two other characterized lactic acid bacteria, Lactococcus lactis and Lactobacillus plantarum. Through the construction of a genome-scale metabolic model of S. thermophilus, the metabolic differences between the three bacteria were visualized by direct projection on a metabolic map. The comparative analysis revealed the minimal amino acid auxotrophy (only histidine and methionine or cysteine) of S. thermophilus LMG18311 and the broad variety of volatiles produced from amino acids compared to the other two bacteria. It also revealed the limited number of pyruvate branches, forcing this strain to use the homofermentative metabolism for growth optimization. In addition, some industrially relevant features could be identified in S. thermophilus, such as the unique pathway for acetaldehyde (yogurt flavor) production and the absence of a complete pentose phosphate pathway.

Attributes and consumer acceptance of yoghurt flavoured with non-cultivated indigenous Swazi fruits

The value of non-cultivated indigenous fruits as flavouring agents for yoghurt has not been given sufficient attention in Swaziland. Consequently, commercial cultivated fruits are used as yoghurt flavours, resulting in higher production costs for the dessert. A study of sensory and physical characteristics of yoghurt flavoured with selected non-cultivated indigenous fruits was done. Fruit purees were made from tincozi, tineyi, and umfomfo, along with mixtures of strawberry, tincozi and tineyi; umfomfo and strawberry; and umfomfo and passion fruit. The physico–chemical properties measured were pH, titratable acidity and potential for syneresis. Sensory evaluation was done by an untrained panel consisting of available, local consumer folks used to doing sensory evaluation and the organoleptic characteristics assessed were appearance, texture and general acceptability. In all cases there were no significant (P > 0.05) changes in pH after 7 days of storage at 4oC. Using indigenous fruit purees did not negatively affect the titratable acidity content of yoghurt. Indigenous fruit flavoured yoghurt had a lower acidity than plain and strawberry flavoured yoghurt. Using indigenous fruits as flavouring agents reduced potential for syneresis significantly (P Keywords : Indigenous fruits, yoghurt, sensory evaluation. AJFAND Vol. 9 (1) 2009: pp. 637-651

Preferences for Commercial Strawberry Drinkable Yogurts Among African American, Caucasian, and Hispanic Consumers in the United States

The drinkable yogurt marketplace is a competitive and growing category in the dairy industry. Understanding sensory differences is critical for understanding the product, and ultimately, consumer preference. The objective of this study was to identify and define the sensory characteristics of commercial drinkable yogurts and link these specific sensory attributes to consumer preferences among Caucasian, African American, and Hispanic consumers in the United States. Focus groups with each ethnic group (n = 10 for each group) were conducted to gain insights into perceptions of drinkable yogurts. A descriptive sensory language was identified to document the sensory properties (visual, flavor, and mouthfeel) of drinkable yogurts. Thirteen commercial drinkable yogurts (strawberry flavor) were subsequently evaluated by a trained sensory panel using the developed sensory language. Five representative yogurts were chosen for consumer testing by each ethnic group (minimum of 75 consumers per group). Both internal and external preference mapping was conducted to identify key drivers of liking. Drinkable yogurts were differentiated by descriptive analysis in visual, flavor, and mouthfeel attributes. Variability was observed in consumer acceptability across the 3 ethnic groups, but these differences were small compared with differences observed among 3 identified consumer preference clusters regardless of ethnicity. Key drivers for all 3 clusters were natural strawberry flavor/aroma and sweet taste. The influence of intensity changes in these 3 drivers along with the presence or absence of other attributes differentiated the 3 clusters. Acceptability varies widely among consumers, and drinkable yogurts with specific flavor and physical properties could be marketed to specific target market segments. The results indicate that these consumer clusters are not defined solely by ethnicity.

Influence of Starter Culture on Flavor and Headspace Volatile Profiles of Fermented Whey and Whey Produced from Fermented Milk

Rennet whey and skim milk were compared as media for fermentation by commercial cheese, yogurt, and probiotic starter cultures. Effect of culture, medium, and their interaction on flavor was assessed and compared by sensory descriptive analysis and headspace volatile analysis by proton transfer reaction-mass spectrometry. In general, the aroma of fermented whey was similar to that of whey separated from fermented milk, indicating a favorable possibility of substituting milk with whey in the manufacture of fermented milk-like beverages. Starter culture significantly affected most sensory characteristics of the products. Key volatile compounds for the characteristic flavor of yogurt, such as acetaldehyde and diacetyl, were not significantly affected by medium when fermented with the yogurt culture, and reached similar levels in both systems. Volatile analysis results were consistent with the results of the sensory evaluation, indicating the high reliability of proton transfer reaction-mass spectrometry in detecting important volatile compounds for aroma. Integration of this sensory and chemical information allows a better understanding of how flavor and related compounds are affected by ingredients or processing, which may be useful for the development of value-added whey products.

Effect of milk fat replacement by polyunsaturated fatty acids on the microbiological, rheological and sensorial properties of fermented milks

AbstractA modified milk (W3DD) where fat had been replaced by oils enriched in ω‐3 polyunsaturated fatty acids was used for the manufacture of a set‐type fermented product. In order to improve the organoleptic properties of the product, 30 g l−1 whey protein concentrate (WPC) was added during the manufacturing process. Samples were fermented employing a commercial probiotic starter culture (ABT‐2), which contained Streptococcus thermophilus ST‐20Y, Lactobacillus acidophilus LA‐5 and Bifidobacterium lactis BB‐12. The acidification process was dependent on the WPC addition, which favoured the increase of viable counts, but fermentation was not influenced by the milk fat composition. The highest counts of the probiotic strains, L acidophilus LA‐5 (3.3 × 105 cfu g−1) and B lactis BB‐12 (5.5 × 107 cfu g−1), after 21 days of storage at 4 °C, were found in fermented products derived from W3DD supplemented with WPC. Addition of WPC also increased the firmness of the products and reduced syneresis. No apparent colour changes due to fat composition or WPC supplementation were observed in the products. Milk fat replacement by oils rich in ω‐3 polyunsaturated fatty acids had a negative influence on the product texture but did not affect the typical yoghurt flavour. These defects were overcome by the addition of 30 g l−1 WPC, which improved the appearance, texture and general acceptability scores in the product. Copyright © 2004 Society of Chemical Industry

Flavor release and rheology behavior of strawberry fatfree stirred yogurt during storage.

The influence of storage on the aroma release in headspace and rheological properties in strawberry-flavored fatfree stirred yogurts was determined. Three periods of storage at 10 degrees C were chosen for analysis: 7, 14, and 28 days. The headspace composition was assessed in a flask in static mode. The SPME fiber was carefully chosen, and results are presented in detail (choice and degradation). The flow properties of the final product were measured in order to follow n (flow behavior index) and K (consistency index), and the apparent viscosity was determined (eta in Pa.s). The quantity of flavors in the headspace of products at the 28 days of aging was significantly weaker for methyl 2-methyl butanoate, ethyl hexanoate, and hexyl acetate. The decrease was half of that in comparison with the seventh day. It was supposed that modification in rheological parameters can partly explain these results. Indeed, the apparent viscosity of the products significantly increased during the three times of storage. The composition of the flavored yogurt, proteins, exopolysaccharides, and fruit preparation, seemed to have a great impact on the release of aroma compounds. The aroma compound amount in the headspace decreased when the matrix changed from water to yogurt. With the fruit preparation, the headspace amounts for esters were significantly lower than in water alone, respectively, 23, 27, 29, and 17% less for methyl 2-methylbutanoate, ethyl hexanoate, hexyl acetate, and benzyl acetate. In flavored yogurt, the amount of aroma compounds in the headspace decreased again in comparison with the result obtained with the fruit preparation. Ethyl hexanoate and hexyl acetate presented the higher decreases of 48 and 53%, respectively.

Impact of engineered Streptococcus thermophilus trains overexpressing glyA gene on folic acid and acetaldehyde production in fermented milk

The typical yogurt flavor is caused by acetaldehyde produced through many different pathways by the yogurt starter bacteria L. bulgaricus and S. thermophilus. The attention was focused on one specific reaction for acetaldehyde and folic acid formation catalyzed by serine hydroxymethyltransferase (SHMT), encoded by the glyA gene. In S. thermophilus, this enzyme SHMT also plays the typical role of the enzyme threonine aldolase (TA) that is the interconvertion of threonine into glycine and acetaldehyde. The behavior of engineered S. thermophilus strains in milk fermentation is described, folic acid and acetaldehyde production were measured and pH and counts were followed. The engineered S. thermophilus strains StA2305 and StB2305, have the glyA gene (encoding the enzyme serine hydroxymethyltransferase) overexpressed. These engineered strains showed normal growth in milk when it was supplemented with Casitione. When they were used in milk fermentation it was observed an increase in folic acid and in acetaldehyde production by StA2305 and for StB2305 it was noticed a significative increase in folic acid formation.

Cheddar whey processing and source: II. Effect on non‐fat ice cream and yoghurt1

SummaryCheddar whey obtained from milk from either a Jersey (J) or a mixed (M) herd was used to observe the effect of whey source (WSr) and whey processing (WPr) on dairy product quality. These were (i) ultrafiltered, vacuum‐evaporated and spray‐dried after lactose crystallization (UFVECSD) and (ii) vacuum‐evaporated and spray‐dried after lactose crystallization (VECSD). These were used to replace non‐fat dry milk (NDM) in vanilla‐flavoured non‐fat yoghurt and non‐fat ice cream at 20, 60, 80 and 90% (w/w solids). Physicochemical and sensory properties of products were assessed on days 1, 15 and 30. In yoghurt, regardless of WSr, pH and titrable acidity were similar in treatments compared to control. All whey protein concentrates (WPCs) decreased apparent viscosity and syneresis. Conversely, penetration increased with increased WPC usage. All, except 20% VECSD, detrimentally affected texture. Syneresis was improved by both WSr and WPr but was better improved by WPr; UFVECSD was the best with regard to syneresis reduction. Yoghurt flavour appeared WSr dependent with J‐WPCs improving it most. On the contrary, texture appeared WPr dependent with all VECSDs markedly improving this parameter. In non‐fat ice cream, all WPCs decreased mix pH and increased centrifugal drainage. Jersey VECSD decreased apparent viscosity at >60% usage. Both UFVECSDs at 60% usage level improved melting resistance. Body and texture were improved by all VECSDs showing significant influence of WPr. Data indicated that both WSr and WPr impacted different attributes of dairy product quality.

Yogurt Thickness: Effects on Flavor Perception and Liking

ABSTRACT:Nine flavored stirred‐style yogurts (thick and thin textured, colored and uncolored, flavored as either cotton candy, lemon‐lime, or strawberry) were evaluated by 120 panelists aged 11 to 14 y to analyze the interactive effects of flavor, thickness, and color on thickness intensity, flavor intensity, and degree‐of‐liking. Yogurt flavor did not affect thickness intensity nor liking ratings. Yogurt thickness did not affect flavor intensity, but flavor liking was affected by both flavor and thickness. Strawberry yogurt was liked equally in both texture systems, but cotton candy and lemon‐lime yogurts were liked more in a thick textured yogurt than a thin yogurt. Colored yogurts were thicker and more flavorful than uncolored yogurts.

Effects of enzymatic modification of milk proteins on flavour and textural qualities of set yoghurt

Milk proteins were enzymatically modified, using neutrase and trypsin immobilised on CM-Sephadex C-50, to the extent of 3, 4 and 5% degrees of hydrolysis. The neutrase-treated milk and the trypsin-treated milk were used separately to prepare set yoghurt. The set yoghurt prepared from neutrase-treated milk showed an improvement in body, texture and flavour, a faster rate of acid development and a reduction in setting time compared with the control. However, the set yoghurt prepared from trypsin-treated milk showed either a small or no improvement in textural and sensory properties. © 2000 Society of Chemical Industry

Probiotic Culture Survival and Implications in Fermented Frozen Yogurt Characteristics

Low-fat ice cream mix was fermented with probiotic-supplemented and traditional starter culture systems and evaluated for culture survival, composition, and sensory characteristics of frozen product. Fermentations were stopped when the titratable acidity reached 0.15% greater than the initial titratable acidity (end point 1) or when the pH reached 5.6 (end point 2). Mix was frozen and stored for 11 wk at –20°C. The traditional yogurt culture system contained the strains Streptococcus salivarius ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The probiotic-supplemented system contained the traditional cultures as well as Bifidobacterium longum and Lactobacillus acidophilus. We compared recovery of Bifodobacterium by three methods, a repair-detection system with roll-tubes and plates on modified bifid glucose medium and plates with maltose + galactose reinforced clostridial medium.Culture bacteria in both systems did not decrease in the yogurt during frozen storage. The roll-tube method with modified bifid glucose agar and repair detection system provided at least one-half log10 cfu/ml higher recovery of B. longum compared with recoveries using modified bifid glucose agar or maltose + galactose reinforced clostridial agar on petri plates. No change in concentrations of lactose or protein for products fermented with either culture system occurred during storage. Acid flavor was more intense when product was fermented to pH 5.6, but yogurt flavor was not intensified. The presence of probiotic bacteria in the supplemented system seemed to cause no differences in protein and lactose concentration and sensory characteristics.

Essential fatty acids in the nutrition of severely neurologically disabled children.

Essential fatty acids (EFA) are important for the normal development and functioning of the brain, retina and immune competent cells. Severely neurologically handicapped children often have feeding difficulties, and the composition of the diet may be critical with respect to an optimal nutrient content. The aim of the present investigation was to evaluate if the dietary intakes and serum phospholipid concentrations of EFA were adequate in a group of severely neurologically impaired children in an institution. To achieve this, a prospective study was done. The investigation showed low dietary intakes of both n-6 fatty acids (FA) and n-3 FA. The serum concentrations of total n-6 FA, linoleic acid and 22:6n-3 (docosahexaenoic acid) as proportions of the total serum phospholipid FA concentration were initially low. The serum concentrations of 20:3n-9 and 22:5n-6 cholesterol, triacylglycerol, total saturated FA, total monounsaturated FA and apolipoproteins A-I and B were high compared with levels in a reference group of healthy children. Following supplementation with fish oil and soyabean oil, the serum lipid profile approached normal. We conclude that the study children had suboptimal intakes of EFA and that elevated serum concentrations of 20:3n-9 and 22:5n6 were useful serological markers of suboptimal EFA status. Recommended dietary allowances for EFA given as a percentage of energy underestimate EFA requirements in children with a low energy intake. Severely disabled children with feeding difficulties should probably be monitored with serum phospholipid FA measurements or calculation of dietary absolute intakes of EFA.

Effects of flavour amplification of Quorn® and yoghurt on food preference and consumption in relation to age, BMI and odour perception

Since the food habits of many elderly people are inadequate, the first experiment of the present study tested whether flavour amplification induces changes in preferences for and consumption of food and thus might result in a nutritional benefit. Two panels, one of 260 and one of 120 subjects, aged 19-98 years, took part in the study in which preferences for flavour-amplified yoghurt and Quorn were measured. For both products, only a few of the young subjects (20%) preferred the high flavour level; the percentage of subjects preferring the high flavour levels increased with age. These changes were highly significant. In a second experiment, participants received, under ad libitum conditions over 2 d in random order, a dish of yoghurt with either a high or a low flavour level. When adjusted for total consumption quantity, consumption of the highly flavoured yoghurt was not significantly correlated with age (r -0.03, P = 0.35). In a third experiment, odour perception was measured by determining the detection threshold for isoamylacetate. BMI values were obtained and the relationships between BMI and odour perception, age, preference and consumption were assessed in the age group 40-65 years. A significant correlation was observed between age and BMI (r 0.51, P < 0.0005). No significant correlation was observed between BMI and relative consumption of highly flavoured yoghurt (r -0.14, P = 0.14). A significant correlation was observed between BMI and preference for flavour-amplified yoghurt (r 0.35, P < 0.001). However, no significant correlation was observed between BMI and odour perception (r 0.07, P = 0.32). With increasing age, a combined influence of age, sex, BMI and odour perception on food preference is to be expected. According to our multiple regression analysis, BMI showed a significant partial regression coefficient (standardized beta 0.36, P = 0.03). In conclusion, flavour amplification of food for older adults deserves attention, but specific approaches, which are tailored to the candidate food systems and older adult target groups, are needed.

Sensory investigation of yogurt flavor perception: mutual influence of volatiles and acidity.

The sensory properties of traditional acidic and mild, less acidic yogurts were characterized by a trained panel using a descriptive approach. Many of the descriptive attributes varied almost linearly with pH, showing either a positive or negative correlation with increasing acidity. The panel was very sensitive to acidity differences, as demonstrated by the linear relationship between acidity perception and pH. Important flavor differences were found between the two classes of yogurt. They were mainly due to differences in acidity and not to different concentrations of the three impact aroma compounds, acetaldehyde, 2,3-butanedione, and 2, 3-pentanedione. This emphasizes the importance of acidity in yogurt flavor. Deodorization and impact aroma compound addition had much less influence on yogurt flavor than pH variations.

Effects of enzymatic modification of milk proteins on flavour and textural qualities of set yoghurt

Milk proteins were enzymatically modified, using neutrase and trypsin immobilised on CM-Sephadex C-50, to the extent of 3, 4 and 5% degrees of hydrolysis. The neutrase-treated milk and the trypsin-treated milk were used separately to prepare set yoghurt. The set yoghurt prepared from neutrase-treated milk showed an improvement in body, texture and flavour, a faster rate of acid development and a reduction in setting time compared with the control. However, the set yoghurt prepared from trypsin-treated milk showed either a small or no improvement in textural and sensory properties. © 2000 Society of Chemical Industry

Fun Microbiology: Making Plain &amp; Frozen Yogurt

Yogurt is one of the oldest fermented milk products known. It is believed to have originated approximately 4,000 years ago in the Middle East (the name comes from Turkish) and spread with the migration of herdsmen in search of water and pastures to stake a living (Vedamuthu 1993). Although yogurt has a long history, its popularity and growth in sales in the United States has occurred primarily over the last 20 years. This could be attributed (but not limited) to the following developments: use of sweeteners to mute tart acid flavor of plain yogurt, introduction of fruits and nuts, inclusion of low-fat and non-fat yogurts containing non-nutritive sweeteners with advertising aimed at calorie-conscious persons, introduction of frozen yogurt as a low-calorie dessert, and accumulation of scientific data indicating health benefits of yogurt consumption (Halpem et al. 1991; Isolauri et al. 1991; Pochart et al. 1989; Vedamuthu 1993). Yogurt is a solid, custard-like milk product fermented with a mixture of the bacteria Streptococcus salaivarius subsp. thermophilus (coccus shaped) and Lactobacillus delbrueckii subsp. bulgaricus (rod shaped)(Atlas 1997; Jay 1996). The pairing of coccus and rod is important in yogurt production because there is an associative beneficial relationship formed between these two bacteria, which in biology is referred to as symbiosis. Modern cultured yogurt production usually begins with concentrating milk by 1/4 volume in a vacuum pan by heating at 90? C (1940 F) for a few minutes. The milk is fortified at 380

Application of Ultrafiltered Sweet Buttermilk and Sweet Buttermilk Powder in the Manufacture of Nonfat and Low Fat Yogurts

Nonfat and low fat yogurts are soft, low in solids, and exhibit whey separation unless they are heavily stabilized. In this study, the quality of nonfat (9.55 to 10.39% total solids) and low fat (13.40%) yogurts that had been fortified with ultrafiltered sweet buttermilk or buttermilk powder was compared with that of a control yogurt that had been fortified with nonfat dry milk. The titratable acidity and pH of low fat yogurts were higher than those of nonfat yogurts. Low fat yogurt that had been fortified with ultrafiltered sweet buttermilk had the highest pH and titratable acidity. As shearing speed increased, the apparent viscosity of yogurts decreased, indicating a shear thinning property. At a high shearing speed, shearing time had little effect on the apparent viscosity. Nonfat yogurts with tested ingredients were similar to the control in flavor, appearance, texture, aroma, smoothness, and sourness. At a high level of fortification, ultrafiltered sweet buttermilk lacked typical yogurt flavor but had good appearance. The microstructures of nonfat yogurts were more open than those of low fat yogurts, possibly because of the higher protein contents of the latter. Ultrafiltered sweet buttermilk yielded the densest matrix. The addition of up to 4.8% sweet buttermilk powder to low fat yogurt mixes yielded a soft and smooth product.

Manufacture and Quality of Iron-Fortified Yogurt

Yogurts (nonfat and low fat) were manufactured and fortified with 10, 20, and 40mg of iron/kg of yogurt. Growth of starter culture bacteria and non-starter culture bacteria as well as lipid oxidation of the yogurts were monitored over 30 d of storage at 4°C. Sensory characteristics of the yogurts were determined during that time by a trained panel of judges, and consumer panels were used to test acceptability of iron-fortified yogurt.Counts of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus after 1 d of storage in iron-fortified skim yogurts were 7.0 x 108 cfu/ml, which were not significantly different from numbers in unfortified yogurts. Counts decreased to 2.5 x 108 and 1.9 x 108 cfu/ml for L. delbrueckii ssp. bulgaricus and S. thermophilus, respectively, after 30 d of storage. Fortifying yogurt with iron did not support the growth of Pseudomonas flurescens or Escherichia coli.No significant increases in chemical oxidation, as measured using the thiobarbituric acid assay, were detected as a consequence of iron fortification. Trained panelists scored all yogurts for oxidized, metallic, bitter, and other off-flavors in the range of “not perceptible” to “very slightly perceptible”. Iron-fortified yogurts had slightly higher oxidized flavor scores than did the control yogurt. There was no increase in metallic, bitter, or other off-flavors. The consumer panel did not detect any significant differences in the appearance, mouthfeel, flavor, or overall quality between fortified and unfortified flavored yogurts. All yogurt samples were liked by the consumer panelists, suggesting that yogurt is a suitable vehicle for iron fortification.

Optimization of Yogurt Production Using Demineralized Whey

ABSTRACTThe effect of three independent fermentation variables: demineralized whey powder (0.0; 1.5 and 3.0%), lactic culture concentration (1.0; 2.0 and 3.0%) and mix treatment temperature (85; 90 and 95°C) was studied. Fermentation time to reach pH 4.3, instrumental consistency and appearance, visual consistency and taste of the product were evaluated. Product consistency increased as mix treatment temperature increased and demineralized whey powder decreased. The powder had a stronger influence on instrumental consistency than did temperature. Appearance was better when whey powder was used at 1.4 to 1.6%. Visual consistency decreased as whey powder increased but addition of demineralized whey powder did not negatively affect yogurt flavor.

Determination and Origin of the Aroma Impact Compounds of Yogurt Flavor

Yogurt exhibits a delicate and low intense flavor which requires mild sample isolation techniques and sensitive identification means. This paper decribes the application of two new flavor separation techniques: combined static and dynamic headspace, and preparative simultaneous distillation−extraction under vacuum. Of the 91 components identified by mass spectrometry, 21 were found to have a major impact on the aroma using a new method for the treatment of GC−sniffing data. One of these compounds, 1-nonen-3-one, was identified by spectral means for the first time in a flavor. Its odor detection threshold of 8 pg/kg appears to be one of the lowest among known flavor compounds. On the basis of the peak areas of yogurt and milk aromagrams, some compounds seem to be already present in milk, others appear to be generated by the strains. Keywords: Yogurt aroma; headspace; GC−olfactometry; impact-compound; composition