The effect of transglutaminase concentration on the texture, syneresis and microstructure of set-type goat's milk yoghurt during the storage period

Instant stevia powder as a novel potential additive for enhancing nutritional value and quality characteristics of yogurt

In the current study, yogurts containing instant stevia powder (ISP) at varying proportions (0.1, 0.2, 0.3, and 0.4 g/100 mL) were perused in terms of physicochemical attributes, textural behavior, antioxidant activity, and sensory acceptability during 14 day storage at 4 °C. For this, bioactive components extracted by using microwave-assisted system were spray dried in optimum conditions (11 mL/min flow rate and 167 °C inlet air temperature) and then incorporated into yogurts. The minimal syneresis value (17.09 g/100 g) at the day of 14 was detected in ISP (0.4 g/100 mL)-supplemented yogurts while this value was reached to 19.45 g/100 g in control counterpart without stevia powder. Enriching yogurts with powders was a plausible way for boosting their mechanical properties. The antioxidative parameters namely total phenolic content (TPC), DPPH, ABTS, FRAP, and CUPRAC values were tendency to increase with ISP increment in yogurts. Low scores in sensory evaluation were detected in yogurts loaded with ISP above a certain amount (more than 0.2 g/100 mL). Sum up, the findings proved that the hypotheses (fabricating innovative dairy product rich in bioactive substances and maintaining quality parameters of yogurts during storage) predicted for this study were successfully achieved.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05892-z.

Properties of Yoghurt Fortified in Lactoferrin with Effect of Storage Time

The stability of fortified yoghurts during refrigerated storage is important for industry and the consumer. The aim of the study was to evaluate the nutritional value, microbiological quality, organoleptic properties, and structure of natural yoghurts made with the addition of lactoferrin during refrigerated storage. In this study, we produced natural yoghurts fortified in lactoferrin, using YC-X11 yoghurt starter culture based on Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Physicochemical (acidity, nutritional value and structure) as well as microbiological and organoleptic changes occurring during 28-days refrigerated storage were determined. Storage research made it possible to determine the direction of changes taking place in the products. The analysed parameters did not differ statistically significantly between the control yoghurts and those with the addition of lactoferrin. Textural and rheological studies also shown that the addition of lactoferrin did not significantly change the structure of the yoghurt. The yoghurts were characterized by high sanitary and hygienic quality during the whole refrigerated storage. Lactoferrin has a positive effect on the durability of the product.

Fucoxanthin as a Biofunctional Compound in Goat Milk Yogurt: Stability and Physicochemical Effects

The food industry has increasingly added nutrients and other ingredients to products to enhance their health benefits. Fucoxanthin is recognized for its benefits in mitigating obesity, diabetes, hypertension, and inflammation. Therefore, addition of fucoxanthin into goat milk yogurt, its stability, and the physicochemical properties of yogurt during processing and storage was investigated. Yogurts with and without fucoxanthin were manufactured by mixing goat whole milk (82.85%, w/w), powdered goat milk (10.68%, w/w), and sugar (6.47%, w/w). Fucoxanthin (0.052 mg/g of yogurt mix) was added to the treatment. The mix was heated at 80 °C for 30 min, cooled, inoculated with a culture, and incubated at 43 °C for 5 h. Fucoxanthin in the yogurt mix and yogurt was quantified by an HPLC method. The recoveries of fucoxanthin from the mix before and after heating were 98.25% and 98.83%, respectively. However, less fucoxanthin (90.13%) was recovered from the freshly prepared yogurt than from the mix. Heating the yogurt mix did not affect the concentration of fucoxanthin but adding the inoculum to the mix reduced its concentration during fermentation. During the storage period, the concentration of fucoxanthin in yogurt remained the same. Fucoxanthin did not adversely affect the chemical composition and physicochemical properties of yogurt, but it influenced the color, decreasing lightness (81.47 ± 0.09), and increasing redness (7.67 ± 0.09) and yellowness (38.24 ± 0.09). Thus, goat milk yogurt can be an effective food matrix to deliver fucoxanthin to human diet.

Quinoa flour as a skim milk powder replacer in concentrated yogurts: Effect on their physicochemical, technological, and sensory properties

Milk standardization with solids (i.e., nonfat milk solids, MSNF) for yogurt manufacture is traditionally achieved by the addition of skim milk powder (SMP). However, the addition of SMP to milk‐based yogurt increases lactose content and decreases both protein content and gel firmness. Thus, in this work, quinoa flour (QF; 0%, 25%, 50%, 75%, and 100% w/w) was used to replace SMP in concentrated yogurt. The physicochemical, textural, and sensory properties and microstructure of the yogurt were evaluated during cold storage. Generally, protein content, water‐holding capacity, and L* value decreased, while syneresis, textural attributes, and viscosity increased with increasing QF content. The substitution of high levels of QF (>25%, w/w) for SMP led to significantly shorter fermentation times, as compared to the control sample. The scanning electron microscopy observations showed significant changes in the yogurt microstructure as a consequence of QF replacement. Samples with 25% (w/w) substitution of QF and control had the highest scores in overall acceptance. According to the results, QF could be applied as an interesting raw material for concentrating the milk‐based yogurt at substitution level of 25% (w/w).

Rheological and textural properties of goat's milk set-type yoghurt as affected by heat treatment, transglutaminase addition and storage

BACKGROUND

Production of goat's milk set-style yoghurt encounters challenges in achieving the texture characteristic for this type of product, primarily due to protein composition of this milk. This study evaluated the effects of using microbial transglutaminase (mTGase) concomitantly with starter culture in the production of goat's milk yoghurt - a method that has not been employed with this milk type until now- indicating the potential of the enzyme to change yoghurt's textural properties. Goat's milk set yoghurts were produced from milk heated at 72 °C/30 s and 90 °C/5 min, without (G72 and G90) and with mTGase (G72TG and G90TG) and starter culture addition. Protein profiles of goat's milks and yoghurts were also examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Yoghurts were evaluated for rheological properties, texture, microbiological and sensory profile over 2 weeks to study the influence of mTGase, pasteurization and storage.

RESULTS

The enzyme caused significant increases of storage moduli at the end of fermentation: 8.32 ± 0.27 Pa (G90TG) and 2.89 ± 0.18 Pa (G72TG) vs. 6.13 ± 0.07 Pa (G90) and 1.27 ± 0.18 Pa (G72) without enzyme. Lower loss tangent values indicated the enhanced elastic character of the gels with enzyme. Enzyme increased yoghurt's firmness from 49.69 ± 2.61 g (G90) to 60.81 ± 5.29 g (G90TG) after 1 day and from 58.21 ± 0.53 g (G90) to 80.45 ± 0.59 g (G90TG) after 15 days' storage. Enzyme improved starter bacteria survivability during storage of G72TG yoghurt.

CONCLUSION

mTGase can be used simultaneously with the starter culture to improve the rheological properties and texture of goat's milk yoghurt, without deteriorating effect on its flavour. © 2021 Society of Chemical Industry.

Effect of Supercritical Extract from Black Poplar and Basket Willow on the Quality of Natural and Probiotic Drinkable Yogurt

Yogurt is a fermented milk drink produced by Streptococcus thermophilus, Lactobacillus delbrüeckii ssp. bulgaricus, or Lactobacillus rhamnosus, which can be enriched with polyphenolic compounds to enhance its antioxidant properties. Supercritical (scCO2/H2O) extracts obtained from the mixture of bark and wood of black poplar (Populus nigra) and basket willow (Salix viminalis) are the source of bioactive compounds. The aim of the study was to assess the effect of supercritical extracts from the P. nigra and S. viminalis on the fermentation, quality, and bioactive properties of drinkable natural and probiotic yogurts. The incorporation of scCO2/H2O extracts at a dose of 0.01% (w/v) into milk for the production of natural and probiotic yogurts increases their functional properties by enhancing the antioxidant activity without causing negative effects on the physicochemical and organoleptic properties of products. The antioxidant activity of yogurt with scCO2/H2O extract from P. nigra and S. viminalis was higher than control yogurts by 1.3-13.2% and 4.4-37.5%, respectively. The addition of a supercritical S. viminalis extract reduced the time of natural and probiotic yogurt fermentation. Natural and probiotic yogurt with scCO2/H2O extracts added was characterised by a bacterial population size of over 7 log cfu/g, and the microflora was active throughout the cold storage period. FTIR analysis confirmed the presence of scCO2/H2O extracts from P. nigra or S. viminalis in both types of yogurt. A secondary structure analysis confirmed interactions between compounds of scCO2/H2O extract from P. nigra and S. viminalis extract with milk proteins. These interactions affect the compounds' structural and functional properties by changing, e.g., their digestibility and antioxidant properties.

The effect of the addition of microbial transglutaminase before the fermentation process on the quality characteristics of three types of yogurt

The effect of the addition of microbial TGase to milk on selected physical properties of the final product and the viability of lactic acid bacteria cultures during storage at 6 °C for 56 days was studied. Three types of set-style yogurt were made with varying parameters. Weekly analyses included the determination of syneresis and water-holding capacity, texture, pH, and the lactic acid bacteria population. Our research has confirmed that mTGase may be used to stabilize yogurts, although the syneresis, the water-holding capacity of yogurts, and the textural features of yogurts were dependent on the step in the production process at which mTGase was added to milk. The presence of mTGase had no relevance with regard to the acidity of yogurts stored under refrigerated conditions. The addition of mTGase had no effect on lactobacilli, but had a variable effect on Streptococcus thermophilus, depending on the duration of enzymatic activity.

Physicochemical evaluation of low-fat yoghurt produced with microbial transglutaminase

BACKGROUND

Currently consumers demand low-fat or non-fat yoghurt but their physical properties are less attractive than those of full-fat yoghurt. It was reported that microbial transglutaminase (TG) can be used in the production of low-fat yoghurt. The aim of this work was to evaluate the effect of TG on low-fat yoghurt to improve their physicochemical and textural properties to approach to those of full-fat yoghurt. Two TG application methods (addition before fermentation or simultaneous addition with the starter), three dose levels and TG origin were evaluated. Results were compared with commercial low-fat and full-fat yoghurts.

RESULTS

No significant differences between application methods were observed. Simultaneous addition of TG was preferred because additional time-consuming steps are not required. The best dose was 1 U TG g^-1 of protein that allowed a firmness higher (4.25 N) than that of commercial low-fat (3.05 N) and full-fat (4.43 N) yoghurts to be achieved. This implies that intermediate values of TG will permit the same firmness as commercial yoghurts to be obtained. It was observed some differences by the TG origin may be due to excipients.

CONCLUSION

TG may be used to replace stabilizers in the production of low-fat yoghurt as it improves texture and avoids initial syneresis. © 2018 Society of Chemical Industry.

Physicochemical, Nutritional, and Organoleptic Characterization of a Skimmed Goat Milk Fermented with the Probiotic Strain Lactobacillus plantarum C4

The benefits of goat milk, fermented milks, and probiotics for the humans are well documented. In this study, a novel fermented goat milk was manufactured with the putative probiotic strain Lactobacillus plantarum C4 together with L. bulgaricus and Streptococcus thermophilus. Ultrafiltration was chosen as the skimmed milk concentration method because it produced the best viscosity and syneresis and a high casein content. The viability rate of all bacterial strains was >10⁷ cfu/mL, even after 5 weeks of storage or after in vitro gastrointestinal digestion, which is especially important for exertion of the probiotic strain functionalities. This fermented milk is also a good source of nutrients, having a low lactose and fat content, high protein proportion, and good mineral concentration. According to these data and the overall acceptability described by panelists, this fermented milk is a healthy dairy product comparable with commercially available fermented milks.

Transglutaminase Applications in Dairy Technology

Consumers' expectations from a dairy product have changed dramatically during the last two decades. People are now more eager to purchase more nutritious dairy foods with improved sensory characteristics. Dairy industry has made many efforts to meet such expectations and numerious production strategies and alternatives have been developed over the years including non-thermal processing, membrane applications, enzymatic modifications of milk components, and so on. Among these novel approaches, transglutaminase (TG)-mediated modifications of milk proteins have become fairly popular and such modifications in dairy proteins offer many advantages to the dairy industry. Since late 1980s, a great number of researches have been done on TG applications in milk and dairy products. Especially, milk proteins-based edible films and gels from milk treated with TG have found many application fields at industrial level. This chapter reviews the characteristics of microbial-origin TG as well as its mode of action and recent developments in TG applications in dairy technology.

Influence of milk protein cross-linking by transglutaminase on the rennet coagulation time and the gel properties

BACKGROUND

Transglutaminase (TGase) modifies milk proteins by cross-linking of caseins, with increased cheese yield being the main technological benefit. In the present work the influence of TGase addition in different concentrations (0, 1, 2 and 3 U g(-1) protein in the system) and under different incubation conditions (0 h, 40 °C/2 h, 25 °C/4 h and 5 °C/16 h) on the rennet coagulation time (RCT) and the comprehensive rennet gel properties were investigated.

RESULTS

Modification of milk proteins by TGase in a concentration-dependent manner caused longer RCT and lower gel firmness. The highest TGase concentration and incubation at 40 °C for 2 h resulted in the longest RCT and the lowest gel firmness. Rennet gels obtained from TGase modified milk were characterised by significantly lower values of texture parameters, lower syneresis and were composed of smaller casein micelles, thinner chains and smaller clusters than those obtained from the control milk. The content of whey proteins in the gel from modified milk was higher and the content of individual casein fractions in the milk samples and rennet gels decreased upon TGase modification.

CONCLUSION

Rennet cheese with modified textural and nutritional properties and improved yield can be obtained upon TGase modification but simultaneous addition of rennet and TGase is recommended. © 2015 Society of Chemical Industry.