Homogenisation improves the microstructure, syneresis and rheological properties of buffalo yoghurt

Production and quality evaluation of a novel γ-aminobutyric acid-enriched yogurt

Objective

γ-aminobutyric acid (GABA) is a neurotransmitter inhibitor that has beneficial effects on various health conditions such as hypertension, cognitive dysfunction, and anxiety. In this study, we investigated a novel yogurt naturally enriched with GABA using a Levilactobacillus brevis strain isolated in our laboratory; the specific optimum yogurt production conditions for this strain were determined.

Methods

We isolated an L. brevis strain and used it to produce yogurt naturally enriched with GABA. We explored the optimal conditions to enhance GABA yield, including fermentation temperature, inoculation amount, L-monosodium glutamate (L-MSG) concentration, fermentation time, and sucrose content. We also performed mixed fermentation with Streptococcus thermophilus and evaluated the quality of the yogurt.

Results

Following optimization (43°C, 8% inoculation amount, 1.5 g/L L-MSG, and 8% sucrose for 40 h of fermentation), the GABA yield of the yogurt increased by 2.2 times, reaching 75.3 mg/100 g. Mixed fermentation with S. thermophilus demonstrated favorable results, achieving a GABA yield akin to that found in some commercially available functional foods. Moreover, the viable microbe count in the GABA-enriched yogurt exceeded 1 × 108 cfu/mL, which is higher than that of commercial standards. The yogurt also exhibited a suitable water-holding capacity, viscosity, 3-week storage time, and favorable sensory test results.

Conclusion

This study highlights the potential of naturally enriched GABA yogurt as a competitive commercial yogurt with beneficial health effects.

Perspectives on the yogurt rheology

The oral processing of yogurt is a dynamic process involving a series of deformation processes. Rheological knowledge is essential to understand the structure and flow properties of yogurt in the mouth and to explore its relationship with sensory perception. Yogurt is rheologically characterized as a non-Newtonian viscoelastic material. The rheological properties of yogurt are affected by many factors, from production to consumption. Therefore, rheological measurements are widely used to predict and control the final quality and structure of yogurts. Recent studies focus on the elucidation of the effects of cultures and processes used in production, as well as the design of different formulations to improve the rheological properties of yogurts. Moreover, the science of tribology, which dominates the surface properties of interacting substances in relative motion to evaluate the structural sensation in the later stages of eating in addition to the rheological properties that give the feeling of structure in the early stages of eating, has also become the focus of recent studies. For a detailed comprehension of the rheological properties of yogurt, this review deals with the factors affecting the rheology of yogurt, analytical methods used to determine rheological properties, microstructural and rheological characterization of yogurt, and tribological evaluations.

Effect of protein-glutaminase on the texture, rheology, microstructure and sensory properties of skimmed set-type yoghurt

The effects of enzymatic deamidation by protein-glutaminase (PG) on the texture, rheology, microstructure, and sensory properties of skimmed set-type yoghurt were studied. The proportion of small-particle size milk protein micelles (10-50 nm) increased significantly from 0 to 99.39% after PG deamidation. Cryo-SEM results revealed that PG-treated yoghurt had a denser and less open 3D structure. PG was effective at inhibiting post-acidification during storage at 4 ℃. The water holding capacity of PG-treated yoghurt (0.12 U·mL-1) increased by more than 15%. The fluidity and viscosity of yoghurt were significantly improved with increasing PG dose. Sensory evaluation revealed that PG (0.06 U·mL-1) significantly improved the smoothness and creaminess of skimmed set-type yoghurt, which corresponded to the pastiness in texture. In summary, PG can effectively address the problems of post-acidification, gel fracture, and flavors change in skimmed set-type yoghurt, providing new applications for PG in the food industry.

Effect of the Heat Exchanger Type on Stirred Yogurt Properties Formulated at Different Total Solids and Fat Contents

In this work stirred yogurts were produced using a technical scale pilot in which the cooling step was processed using either a tubular (THX; low shear) or a plate (PHX, high shear) heat exchanger. The aim was to determine how total solids (TS, adjusted using lactose) and fat contents (FC) impact stirred yogurt properties during storage, depending on the heat exchanger used. Using raw milk, cream, skim milk powder, and lactose, four yogurts were formulated at 16.5% TS and 4.2% proteins, with different FC (0.0, 1.3, 2.6, and 3.9%); one more control yogurt was formulated at 14% TS, 4.2% proteins, and 0.0% FC. Analyses of yogurts (firmness, viscosity, induced syneresis) were realized at days 1, 3, 7, 21, and 34 after production. The addition of lactose between the non-fat yogurt at 14 or 16.5% TS had little to no effect on stirred yogurt properties. Increasing FC reduced syneresis while increasing firmness and viscosity. The use of PHX reduced the syneresis compared to THX; however, it also tended to reduce the firmness of the yogurts with 3.9% FC.

Digital technologies to assess yoghurt quality traits and consumers acceptability

BACKGROUND

Sensory biometrics provide advantages for consumer tasting by quantifying physiological changes and the emotional response from participants, removing variability associated with self-reported responses. The present study aimed to measure consumers' emotional and physiological responses towards different commercial yoghurts, including dairy and plant-based yoghurts. The physiochemical properties of these products were also measured and linked with consumer responses.

RESULTS

Six samples (Control, Coconut, Soy, Berry, Cookies and Drinkable) were evaluated for overall liking by n = 62 consumers using a nine-point hedonic scale. Videos from participants were recorded using the Bio-Sensory application during tasting to assess emotions and heart rate. Physicochemical parameters Brix, pH, density, color (L, a and b), firmness and near-infrared (NIR) spectroscopy were also measured. Principal component analysis and a correlation matrix were used to assess relationships between the measured parameters. Heart rate was positively related to firmness, yaw head movement and overall liking, which were further associated with the Cookies sample. Two machine learning regression models were developed using (i) NIR absorbance values as inputs to predict the physicochemical parameters (Model 1) and (ii) the outputs from Model 1 as inputs to predict consumers overall liking (Model 2). Both models presented very high accuracy (Model 1: R = 0.98; Model 2: R = 0.99).

CONCLUSION

The presented methods were shown to be highly accurate and reliable with respect to their potential use by the industry to assess yoghurt quality traits and acceptability. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The roles of brewers' spent grain derivatives in coconut-based yogurt-alternatives: Microstructural characteristic and the evaluation of physico-chemical properties during the storage

Water soluble coconut extract (WSCE) was reported as a suitable matrix for probiotic delivery as yogurt alternatives. The study aimed to evaluate the roles of brewers' spent grain (BSG) derivatives in enhancing the properties of WSCE-based yogurt alternatives. BSG flour (BSGF) and 3 different protein extracts (BSGPs) including protein control (BSGP-C), protamex treatment (BSGP-P), and protamex combined with flavourzyme treatment (BSGP-PF) were incorporated in WSCE-based yogurt alternatives. Confocal laser scanning microscopy showed that BSGPs prepared with protease treatment generated less dense fat distribution and more homogenous globules compared to that in WSCE control yogurt. It also resulted in a softer, denser and more homogenous matrix. The modification in microstructural properties was aligned with differences in several functional groups including ⍺-glycosidic bond and hydroxyl groups from polysaccharides, aliphatic ethers and acid functional groups as well as aromatic hydrocarbons of lignin, amide I, acetyl groups and amide III. BSGF and BSGPs increased the mechanical properties, viscosity and modified flow behaviour properties demonstrating its ability in maintaining textural and gel formation. After 14 days of storage, maintenance in flow behaviour, syneresis and mechanical properties was identified. Furthermore, BSG derivatives enhanced lactic acid production up to 3 folds. In conclusion, BSG derivatives maintained the microstructure and gel formation, improved the properties of WSCE-based yogurt alternatives and preserved its behaviour during 14 days of storage.

Manipulation of the Phenolic Quality of Assam Green Tea through Thermal Regulation and Utilization of Microwave and Ultrasonic Extraction Techniques

The aim of this study was to investigate the catechin levels and antioxidant activities as manipulated by roasting temperature and roasting time of green tea. Roasting temperature and time varied between 100–300 °C and 60–240 s in green tea production. The main interactions measured were effects on the antioxidant activities, total phenolic content, DPPH, ABTS, FRAP and catechin content (catechin (C), epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC)). Optimum roasting conditions were determined as 270 °C for 240 s, since this enabled high catechin contents, antioxidant activities and production yield. The extraction methods for green tea including traditional extraction (TDE), microwave-assisted extraction (MAE) and ultrasonic-assisted extraction (UAE) using 60% ethanol as solvent were investigated to evaluate the highest bioactive compound and yield of extraction. MAE was found to be more efficient in green tea extraction compared to UAE and TDE. The extracts showed significant cytotoxic potential against the Huh-7 cell line, in concentrations ranging from 31.25 to 1000 µg/mL. The results are useful in understanding the relationship between thermal treatment and extraction conditions on the chemical and nutritional properties of tea catechins, making it possible to select the production and extraction conditions that maximize the levels of beneficial tea ingredients.

New Insights into Cheese Microstructure

Microscopy is often used to assist the development of cheese products, but manufacturers can benefit from a much broader application of these techniques to assess structure formation during processing and structural changes during storage. Microscopy can be used to benchmark processes, optimize process variables, and identify critical control points for process control. Microscopy can also assist the reverse engineering of desired product properties and help troubleshoot production problems to improve cheese quality. This approach can be extended using quantitative analysis, which enables further comparisons between structural features and functional measures used within industry, such as cheese meltability, shreddability, and stretchability, potentially allowing prediction and control of these properties. This review covers advances in the analysis of cheese microstructure, including new techniques, and outlines how these can be applied to understand and improve cheese manufacture.

Plant and Dairy-Based Yogurts: A Comparison of Consumer Sensory Acceptability Linked to Textural Analysis

Yogurt, readily available in plant and dairy-based formulations, is widely consumed and linked with health benefits. This research is aimed to understand the sensory and textural spectrum of commercially available dairy and plant-based yogurts. In a preliminary study, qualitative focus group discussions (4 groups; n = 32) were used to determine perceptions of 28 dairy and plant-based yogurts, identifying positive consumer perceptions of plant-based yogurts. A smaller subset of five spoonable and one drinkable yogurts-(Reference, Soy, Coconut, Cookies, Berry, and Drinkable) was subsequently selected for rheological and structural measurements, showing wide variations in the microstructure and rheology of selected yogurt samples. A quantitative blind sensory tasting (n = 117) showed varying yogurt acceptability, with Berry being the least-liked and Cookies being the most-liked yogurt, in terms of overall liking. The multi-factor analysis confirmed that compositional and textural elements, including protein content, gel firmness, and consistency coefficient, displayed a positive relationship with overall liking. In contrast, fat, sugar, and calories were negatively correlated to the overall liking. This research showed that texture and other compositional factors are significant determinants of the consumer acceptability of yogurt products and are essential properties to consider in product development.

The Sensory Quality and the Textural Properties of Functional Oolong Tea-Infused Set Type Yoghurt with Inulin

Set type yoghurts are characterised by a semi-solid texture, which is created during the fermentation process. The tea infusion in this type of yoghurt production can influence the quality of the final product. Therefore, the aim of the experiment was to evaluate the influence of the addition of 3, 6 and 9% inulin to oolong tea-infused yoghurts on the sensory quality. It has been evaluated by trained experts using a Quantitative Descriptive Profile analysis and by consumers using hedonic scaling, as well as on instrumentally evaluated features such as texture, stability and visual parameters. The addition of oolong tea to yoghurt resulted in positive changes in the perception of sweet, peach and nectar odours and flavours, and also creaminess, as well as negative changes in the presence of a bitter taste, the whey presence and a colour intensification towards dark cream (p ≤ 0.05). The addition of inulin to the tested oolong tea yogurts caused a decrease in the whey presence and brightened the yoghurt's colour (6% and 9%, p ≤ 0.05, respectively), as well as an improved creaminess and an increase in the sweet taste of the yoghurt. It was also observed that the addition of oolong tea deteriorated the instrumentally evaluated texture of the set yoghurts, while inulin at a higher concentration (9%, p ≤ 0.05) increased the firmness and adhesiveness. Moreover, the addition of inulin also had a positive effect on the yoghurt's stability. The addition of inulin to oolong tea-infused set yoghurts may be valuable both as a source of prebiotic fibre in functional products and as a factor improving the quality of these products.

Functional Tea-Infused Set Yoghurt Development by Evaluation of Sensory Quality and Textural Properties

In the present study, the potential to design natural tea-infused set yoghurt was investigated. Three types of tea (Camellia sinensis): black, green and oolong tea as well as lemon balm (Melissa officinalis L.) were used to produce set yoghurt. The sensory quality (using Quantitative Descriptive Profile analysis and consumer hedonic test) and texture analysis, yield stress, physical stability and colour analysis were assessed to describe the profile of the yoghurt and influence of quality attributes of the product on the consumer acceptability of infused yoghurts in comparison with plain yoghurt. Among the analyzed plant additives for yoghurt, addition of 2% oolong tea to the yoghurt allows a functional food to be obtained with satisfactory texture and sensory properties, accepted by consumers at the same level as for control yoghurt. Both types of yoghurt were also characterised by high consumer willingness to buy, which confirms the legitimacy of using oolong tea as a natural, functional yoghurt additive that improves the sensory quality of the product. The high overall quality of yoghurt with oolong tea in comparison to other plant extracts was associated with the intensive peach flavour and odour, nectar and sweet odour and flavour, and the highest creaminess and thickness. That was confirmed by principal component analysis (PCA) where the overall sensory quality of yoghurts was mainly positively correlated with peach flavour and odour, sweet odour and yoghurt odour, while it was negatively correlated with herbs flavor and odour, and green tea flavour and odour. The sensory profile confirmed no differences in textural profile between plain yoghurt and the tea-infused one measured in the mouth, which corresponds to the result of textural properties such as firmness and adhesiveness.

Inclusion of Probiotics into Fermented Buffalo (Bubalus bubalis) Milk: An Overview of Challenges and Opportunities

Buffalo-milk-based dairy products provide various health benefits to humans since buffalo milk serves as a rich source of protein, fat, lactose, calcium, iron, phosphorus, vitamin A and natural antioxidants. Dairy products such as Meekiri, Dadih, Dadi and Lassie, which are derived from Artisanal fermentation of buffalo milk, have been consumed for many years. Probiotic potentials of indigenous microflora in fermented buffalo milk have been well documented. Incorporation of certain probiotics into the buffalo-milk-based dairy products conferred vital health benefits to the consumers, although is not a common practice. However, several challenges are associated with incorporating probiotics into buffalo-milk-based dairy products. The viability of probiotic bacteria can be reduced due to processing and environmental stress during storage. Further, incompatibility of probiotics with traditional starter cultures and high acidity of fermented dairy products may lead to poor viability of probiotics. The weak acidifying performance of probiotics may affect the organoleptic quality of fermented dairy products. Besides these challenges, several innovative technologies such as the use of microencapsulated probiotics, ultrasonication, the inclusion of prebiotics, use of appropriate packaging and optimal storage conditions have been reported, promising stability and viability of probiotics in buffalo-milk-based fermented dairy products.

Effects of High-Pressure Homogenization on the Structural, Physical, and Rheological Properties of Lily Pulp

The effects of high-pressure homogenization (HPH) on the structural, physical, and rheological properties of lily pulp (15%, w/w) were investigated. Different pressures ranging from 0 MPa to 100 MPa were used. The focus was on evaluating the changes in the particle size distribution (PSD), structure, pulp sedimentation behavior, serum cloudiness (SC), total soluble solids (TSS), color, and rheological behavior of the pulps. PSD analysis showed that the diameter of suspended lily particles significantly decreased with an increasing homogenization pressure. The suspended particles observed through optical microscopy became small after homogenization, highlighting the effect of HPH on disrupting the suspended particles. Compared with the untreated pulp, the SC and sedimentation velocity of the homogenized pulps decreased due to the disruption of the suspended particles. The effects of HPH on the sedimentation index and SC exhibited an asymptotic behavior similar to that of the changes in the particle size of lily pulp. Moreover, HPH processing reduced the viscosity of lily pulp and increased the TSS and lightness of the homogenized pulps. HPH significantly modified the structural, physical, and rheological properties of lily pulp. The pulp homogenized above 60 MPa had good suspension stability. This finding indicates that HPH technology can be used to improve the stability of lily pulp.

Streptococcus thermophilus APC151 Strain Is Suitable for the Manufacture of Naturally GABA-Enriched Bioactive Yogurt

Consumer interest in health-promoting food products is a major driving force for the increasing global demand of functional (probiotic) dairy foods. Yogurt is considered the ideal medium for delivery of beneficial functional ingredients. Gamma-amino-butyric acid has potential as a bioactive ingredient in functional foods due to its health-promoting properties as an anti-stress, anti-hypertensive, and anti-diabetic agent. Here, we report the use of a novel Streptococcus thermophilus strain, isolated from the digestive tract of fish, for production of yogurt naturally enriched with 2 mg/ml of gamma-amino-butyric acid (200 mg in a standard yogurt volume of 100 ml), a dose in the same range as that provided by some commercially available gamma-amino-butyric acid supplements. The biotechnological suitability of this strain for industrial production of yogurt was demonstrated by comparison with the reference yogurt inoculated with the commercial CH1 starter (Chr. Hansen) widely used in the dairy industry. Both yogurts showed comparable pH curves [ΔpH/Δt = 0.31-0.33 h^-1], viscosity [0.49 Pa-s], water holding capacity [72-73%], and chemical composition [moisture (87-88%), protein (5.05-5.65%), fat (0.12-0.15%), sugar (4.8-5.8%), and ash (0.74-1.2%)]. Gamma-amino-butyric acid was not detected in the control yogurt. In conclusion, the S. thermophilus APC151 strain reported here provides a natural means for fortification of yogurt with gamma-amino-butyric acid.