Effects of various whey proteins on the physicochemical and textural properties of set type nonfat yoghurt

In this study, the changes during storage in the physicochemical, textural and sensory properties of nonfat yoghurts fortified with whey proteins, namely whey protein concentrates (WPC), whey protein isolates and whey protein hydrolysates, were investigated. Enrichment of nonfat yoghurt with the whey protein additives (1% w/v) had a noticeable effect on pH, titratable acidity, syneresis, water‐holding capacity, protein contents and colour values on the 14th day of storage (P < 0.01). The addition of whey proteins to the yoghurt milk led to increases in the hardness, cohesiveness and elasticity values, resulting in improved textural properties. The addition of WPC improved the texture of set‐type nonfat yoghurt with greater sizes in the gel network as well as lower syneresis and higher water holding capacity. This study suggests that the addition of whey protein additives used for fortification of yoghurt gave the best textural and sensory properties that were maintained constant during the shelf life.     

Effects of somatic cell counts on the physicochemical and rheological properties of yoghurt made from sheep’s milk

In the present work, yoghurts were made from sheep’s milk with two different somatic cell count (SCC), at low (200 000 cells mL^?1) and high (750 000 cells mL^?1) levels. The characteristics of the final product were analysed for pH, acidity, protein, total solids, fat, syneresis, water holding capacity (WHC) and apparent viscosity. Samples were analysed on days 1, 7 and 14 after production of yoghurts. The SCC had no significant effect either on the acidity or pH of the yoghurt at 24 h (P > 0.05) but a significant effect (P < 0.05) was observed at 168 h. No effects of SCC were observed on total solids and fat content of the yoghurt after 24 and 168 h. High SCC (HSCC) yoghurt had higher protein content (P < 0.05). The yoghurt with the highest SCC had the highest level of syneresis. Viscosity of HSCC yoghurt was higher than that of the low SCC yoghurt on days 1, 7 and 14 of storage. The flow properties also showed that the low SCC yoghurt was softer than that from milk with high content in somatic cells.     

Stevia‐fortified yoghurt: Stability,antioxidant activity and in vitro digestion behaviour

In this study, yoghurt samples were fortified with 0.25% and 0.5% freeze‐dried stevia extract (FSE). The control and stevia‐fortified yoghurts were evaluated and compared for the viability of the starter cultures, physicochemical properties, total phenolic content (TPC) and antioxidant activity throughout 30 days of storage. In addition, TPC and antioxidant activity were evaluated during in vitro gastrointestinal digestion. The results showed that the yoghurt matrix preserved the TPC, antioxidant capacity and total solids during storage, while the acidity, synaeresis and counts of the starter cultures of the final product were not significantly affected. However, addition of 0.5% FSE exerted a buffering effect on the system. After simulated digestion, the values of TPC and antioxidant activity of the fortified yoghurts increased in relation to the undigested fractions. These findings showed the feasibility of employing FSE as a functional ingredient in the manufacture of yoghurts with potential antioxidant properties.     

Sensory properties of soy yoghurts prepared from yellow and black soymilk using Streptococcus infantarius 12 and Weisellia sp. 4

BACKGROUND: Soy yoghurts containing enhanced bioactive isoflavone aglycones were prepared from combinations of yellow (YS) and black soymilk (BS) (YS:BS = 100:0, 70:30, 50:50 and 0:100, v/v) by fermentation with Streptococcus infantarius 12 and Weisellia sp. 4 at 37 °C for 10 h. Sensory properties of the bioactive soy yoghurts were investigated. Furthermore, other characteristics including the contents of isoflavones, viable cell numbers, pH, colour and DPPH radical scavenging activity were investigated. RESULTS: One hundred percent YS yoghurt showed the highest scores of all sensory attributes while 100% BS yoghurt was the lowest for colour and smoothness. The overall acceptability scores were 5.9 and 5.2 for 100% YS and 100% BS yoghurts, respectively (9‐point scale). The L‐values of soy yoghurts decreased as the percentage BS increased, indicating darkening of soy yoghurts. The contents of bioactive isoflavone aglycones (daidzein and genistein) in soy yoghurts remarkably increased (>1300 mg kg^?1) by fermentation. Viable cell numbers and pH of soy yoghurts ranged from 8.4 × 10⁸ to 9.6 × 10⁸ CFU g^?1 and 4.43 to 4.54, respectively. DPPH radical scavenging activity significantly increased as the percentage BS increased (P < 0.05). CONCLUSION: One hundred percent YS yoghurt was better for overall sensory properties while 100% BS yogurt was more bioactive in terms of the isoflavone aglycone contents and DPPH radical scavenging activity compared to other yoghurts. Copyright © 2008 Society of Chemical Industry     

Effect of papain‐hydrolysed casein peptides on the fermentation kinetics,microbiological survival and physicochemical properties of yoghurt

The objective of this study was to determine the effect of different molecular mass papain‐hydrolysed casein peptides (PCP) on the growth of lactic acid bacteria (LAB) (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in 1:1 ratio) and on the fermentation kinetics, microbiological survival and physicochemical properties in yoghurt. The fraction of PCP4 (<3 kDa) exhibited the highest growth‐promoting activity on the strains. The value of T_pH4.5 (time necessary to reach pH 4.5) of yoghurt fortified with PCP4 reduced from 5.21 to 4.29 h, and the total counts of LAB present in the final products increased from 8.29 to 8.42 log CFU mL^?1 with the addition of PCP4 at nitrogen replaced ratio of 3% (w/w). Moreover, the yoghurt exhibited lower postacidification power, higher viscosity and sensory evaluation scores than did the control product during storage period.     

Physiochemical,textural, sensory properties and probiotic survivability of Chinese Laosuan Nai (protein‐fortified set yoghurt) using polymerised whey protein as a co‐thickening agent

A new Chinese Laosuan Nai (protein‐fortified set yoghurt) was developed using polymerised whey protein (PWP, 0.4%, w/v) as a co‐thickening agent. The prototype was analysed for physiochemical, textural, sensory properties and probiotic survivability and compared with a commercial sample. Experimental yoghurts were significantly higher in pH, protein content, hardness and viscosity (P < 0.01). Microstructure indicated a uniform and denser protein network. Probiotics remained stable for Bifidobacterium during a 10‐week storage period. Results indicated that polymerised whey protein may be a novel protein‐based co‐thickening agent for making Chinese Laosuan Nai.     

Effects of poly‐γ‐glutamic acid on the physicochemical characteristics of skim milk yoghurt

The physicochemical and sensory properties of skim milk yoghurts containing poly‐γ‐glutamic acid (PGA) at different levels (0.0025, 0.005 and 0.01%) were evaluated. Addition of PGA up to 0.01% to reconstituted skim milk (11%, w/v) did not affect the growth of lactic acid bacteria or the development of titratable acidity in yoghurt, whereas full‐fat control yoghurt had reduced acid production. No changes were found in viable cell counts of PGA yoghurts during storage (4 weeks at 4 °C). The addition of PGA (0.005%) significantly decreased syneresis in skim milk yoghurt and did not cause any undesirable effects in sensory acceptability.     

Effects of different prebiotic stabilisers and types of molasses on physicochemical,sensory, colour and mineral characteristics of probiotic set yoghurt

The physicochemical, sensory, properties and mineral profile of probiotic set yoghurts prepared with different prebiotic stabilisers (pectin and guar) at 0.5% (w/v) and different molasses (grape, mulberry and carob) at 10% (v/v) were investigated. Guar‐supplemented yoghurts had the lowest titratable acidity values (P < 0.01) also the highest water‐holding capacity values (P < 0.01). However, guar had a negative effect on gel firmness and sensory properties of yoghurts. The effect of different stabilisers and molasses on colour L* and a*values was statistically significant (P < 0.01). Panelists gave the highest flavour scores to the pectin‐added yoghurts during storage period (P < 0.01).     

The effect of hydrolysed tragacanth gum and inulin on the probiotic viability and quality characteristics of low‐fat yoghurt

This study investigates the effect of supplementation of tragacanth gum (GT, 0.05% w/v), low molecular weight gum tragacanth (LMWGT, 0.5% w/v) and inulin (0.5% w/v) on the viability of Bifidobacterium bifidum and the quality parameters of low‐fat yoghurt during a three‐week storage period. The count of probiotics was found to be 7.8 log cfu/g in inulin, and LMWGT enriched yoghurts at the end of the storage period. The minimum water holding capacity and the maximum syneresis values were also obtained in the low‐fat yoghurt enriched with GT throughout the storage time. The samples containing inulin and LMWGT revealed sensory attributes that were judged superior compared to those in GT.     

Folic acid fortified fat-free plain set yoghurt

The objective was to elucidate the effect of folic acid incorporation on the physico-chemical and sensory characteristics of yoghurt. Folic acid was added during mix preparation (before pasteurization) or immediately after culture addition (after pasteurization) at 25 and 50% of the recommended dietary allowance (RDA) of 300 µg. Folic acid fortified yoghurts were significantly different from the control and were yellowish. The pH and titratable acidity (TA) values of folic acid fortified yoghurts remained unchanged compared to the control. Folic acid fortified yoghurts had significantly lower flavour, body and texture scores and better water-holding capacity compared to the control.     

The physicochemical properties of yoghurt supplemented with microencapsulated peanut sprout extract,a possible functional ingredient

This study was designed to determine the physicochemical and sensory properties of yoghurt supplemented with powdered peanut sprout extract microcapsules (PPSEM) (3–10 μm) during storage at 4 °C for 16 days. The releasing rates of the polyphenol, resveratrol, from yoghurts were minimised at lower concentrations of PPSEM (0.25 and 0.5%, w/v). The viscosity decreased gradually with higher concentrations of PPSEM added. In the sensory test, there were significant increases in yellowness, peanut and cooked scores (P < 0.05). Based on the results, it is concluded that the low concentrations (0.25 and 0.50%, w/v) could be used to produce PPSEM‐supplemented yoghurt without significant adverse effects on the physicochemical and functional properties.     

Effect of packaging materials and dissolved oxygen on the survival of probiotic bacteria in yoghurt

The effects of packaging materials on the dissolved oxygen and the survival of the probiotic bacteria in yoghurt were studied. Oxygen adapted and non‐oxygen adapted strains of Lactobacillus acidophilus and Bifidobacterium spp. were incorporated in yoghurts, which were packaged in oxygen permeable high‐impact polystyrene (HIPS), oxygen‐barrier material (Nupak^TM) and Nupak^TM with an oxygen scavenging film (Zero₂^TM). During storage the dissolved oxygen increased steadily in HIPS packaged yoghurt whereas it remained low in yoghurts packaged in Nupak^TM and Zero₂^TM. In all yoghurts, no significant decreases were observed in the viability of either oxygen adapted or non‐oxygen adapted cells of L. acidophilus and Bifidobacterium spp. Thus, although the dissolved oxygen in yoghurt can be influenced by the type of packaging material, it may not affect the survival of probiotic bacteria in yoghurts.     

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

A 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     

Comparison of volatile compounds in yoghurts made from cows’, buffaloes’, ewes’ and goats’ milks

The composition of the volatile fraction of yoghurts made from cows’, buffaloes’, ewes’ and goats’ milks was investigated during the 28 days of storage at 4 °C using solid‐phase microextraction technique (SPME) and gas chromatography coupled to mass spectrometry analysis (GC/MS). A total of 34 volatile compounds were identified in yoghurts during their storage at 4 °C, including aldehydes, ketones, alcohols, esters, acids, terpenes, hydrocarbons and sulphur compounds. In this study, acetaldehyde, diacetyl and acetoin, considered as the major compounds of yoghurt, were detected in all yoghurts.     

Effect of long‐chain inulin on the texture profile and survival of Lactobacillus paracasei ssp. paracasei in set yoghurts during refrigerated storage

The effects of adding inulin at 20 g/L as a fat replacer and probiotic bacteria on the physicochemical and textural characteristics of yoghurt were studied. The ability of long‐chain inulin to improve the probiotic (Lactobacillus paracasei ssp. paracasei) bacteria viability in yoghurt was investigated. The addition of inulin made the texture (firmness, cohesiveness, adhesiveness and gumminess) of skimmed yoghurt similar to that of whole yoghurt, demonstrating the role of inulin as a fat replacer. However inulin increased syneresis and did not influence the viability of probiotic bacteria in the yoghurts. The addition of probiotic bacteria in yoghurts improved syneresis and increased firmness and gumminess.     

Effect of Flavourzyme® on Angiotensin‐Converting Enzyme Inhibitory Peptides Formed in Skim Milk and Whey Protein Concentrate during Fermentation by Lactobacillus helveticus

Angiotensin‐converting enzyme inhibitory (ACE‐I) activity as affected by Lactobacillus helveticus strains (881315, 881188, 880474, and 880953), and supplementation with a proteolytic enzyme was studied. Reconstituted skim milk (12% RSM) or whey protein concentrate (4% WPC), with and without Flavourzyme^® (0.14% w/w), were fermented with 4 different L. helveticus strains at 37 °C for 0, 4, 8, and 12 h. Proteolytic and in vitro ACE‐I activities, and growth were significantly affected (P < 0.05) by strains, media, and with enzyme supplementation. RSM supported higher growth and produced higher proteolysis and ACE‐I compared to WPC without enzyme supplementation. The strains L. helveticus 881315 and 881188 were able to increase ACE‐I to >80% after 8 h of fermentation when combined with Flavourzyme^® in RSM compared to the same strains without enzyme supplementation. Supplementation of media by Flavourzyme^® was beneficial in increasing ACE‐I peptides in both media. The best media to release more ACE‐I peptides was RSM with enzyme supplementation. The L. helveticus 881315 outperformed all strains as indicated by highest proteolytic and ACE‐I activities.     

Effect of different levels of pine honey addition on physicochemical,microbiological and sensory properties of set‐type yoghurt

In this study, the effects of different levels of pine honey addition (3%, 5% and 7% w/v) to the yoghurt milk on starter bacteria, physicochemical and sensory characteristics of set‐type yoghurts during the storage were investigated. Antioxidant activity and total phenolic content of yoghurts with added honey increased compared to control yoghurt. There was a significant increase in water‐holding capacity (WHC), viscosity, total solids, redness (a*) and yellowness (b*) values of the yoghurt samples with the addition of honey at higher concentrations, whereas water activity (aw), pH and luminosity (L*) values decreased. Viscosity and WHC of the yoghurts increased during the storage.     

Ability to detect and identify the presence of particles influences consumer acceptance of yoghurt

The common practice of particle addition into semisolid foods is known to influence sensory textural properties, but the resulting influence on consumer acceptability is not well understood. A systematic trial was therefore designed, involving a set of nine yoghurt samples, to investigate the effect of particle addition on consumer acceptability. Agar microgels were fabricated and added to yoghurt at varying levels of modulus (210 kPa or 550 kPa, fabricated with 5% or 10% agar, respectively), particle size (30 μm or 100 μm) and particle concentration (2% or 5%, w/w). The yoghurt samples were presented to consumers (n = 117), who rated acceptability, and subsequently selected from the attributes particles, drying, sweet, smooth, no particles and none of these by ‘check all that apply’ (CATA), for each sample. On average, all samples were generally well-liked by consumers, although samples containing 5% (w/w) particles were less acceptable than those containing 2% (w/w) particles. Consumer cluster analysis was used to identify groupings of consumers based on difference in acceptability scores. Acceptability scores for the yoghurts were lower for the consumers who selected the attribute particles in the higher modulus samples. Addition of particles (30 μm or 100 μm) at 550 kPa modulus and 5% (w/w) particles was identified as the threshold of particle detection in this yoghurt system and the point at which acceptability scores declined.     

Investigation of the potential for using inulin HPX as a fat replacer in yoghurt production

In this study yoghurts produced from full-fat milk (3.2%) and from low-fat milk (0.5%), with 0.7% and 2.7% added inulin, were compared. Inulin addition did not influence bacterial counts and acidity. Yoghurt from full-fat milk showed the highest values of apparent viscosity, followed by yoghurt with 2.7% of inulin. The sensory properties of the yoghurts differed mainly in terms of texture and taste. The highest scores were gained by yoghurt from full-fat milk, but yoghurt with 2.7% of inulin received only slightly lower scores. The results indicate that inulin has potential as a fat replacer in yoghurt.     

Influence of skimmed milk concentrate replacement by dry dairy products in a low‐fat set‐type yoghurt model system. Use of caseinates,co‐precipitate and blended dairy powders

Yoghurt fortification with caseinates, co‐precipitate and blended dairy powders in a low‐fat yoghurt model system was studied. These dairy products were characterised for pH, moisture, lactose, mineral and protein fractions. Milk proteins were characterised by polyacrylamide gel electrophoresis (SDS‐PAGE) and isoelectric focusing (IEF). Minerals such as Na, Ca, K and Mg were analysed by atomic absorption spectroscopy. Yoghurts were formulated using a skimmed milk concentrate as a milk base enriched with different dry dairy products up to 43 g kg⁻¹ protein content. The percentage of skimmed milk concentrate replaced with dry dairy products in the mix was between 1.37 and 6.35%. Yoghurts enriched with caseinates had higher viscosity and syneresis index (56.81 Pa s and 548.8 g kg⁻¹ respectively) than yoghurts based on concentrated skimmed milk fortified with co‐precipitate (39.00 Pa s and 392.9 g kg⁻¹) or blended dairy products (33.25 Pa s and 431.8 g kg⁻¹). One blended dairy product was tested to manufacture low‐fat yoghurt on an industrial scale, yielding good rheological properties (high viscosity‐consistence, 37.77 Pa s, and low syneresis index, 450 g kg⁻¹) and lower cost than traditional enrichment with skimmed milk powder. © 2000 Society of Chemical Industry