Functional stability of goats' milk yoghurt supplemented with Pistacia atlantica resin extracts and Saccharomyces boulardii

The present study describes the development of a functional goats' milk yoghurt, using Pistacia atlantica resin extracts and Saccharomyces boulardii, in an attempt to combine the beneficial effects of the milk, extract and probiotic microorganisms. Results demonstrated that Pistacia extracts promoted the survival of lactic acid bacteria and NMR spectra additionally revealed that the functional fatty acids can be retained during the shelf life of yoghurts, alongside with the other bioactive compounds. The organoleptic assessment revealed that there were no significant differences in flavour, body, texture and appearance between the different yoghurts.     

Fortification of milk with plant extracts modifies the acidification and reducing capacities of yoghurt bacteria

The acidification and reducing capacities of yoghurt bacteria were evaluated in different plant extract‐enriched milk samples. The milk samples enriched with thyme and grape seed extracts exhibited the highest values of acidification capacity for Lactobacillus delbrueckii subsp. bulgaricus (LB) (0.0065 pH unit/min) and Streptococcus thermophilus (ST) (0.0068 pH unit/min). The highest values of reducing capacity were observed in thyme (?0.98 mV/min), grape (?1.92 mV/min) and green tea (?0.75 mV/min)‐enriched samples for LB, ST and mixed culture of LB + ST, respectively. The fortification of yoghurt with plant extracts modified the acidification and reducing activities of starters, thus changing the fermentation time and quality attributes of the product.     

Fractionation by microfiltration: Effect of casein micelle size on composition and rheology of high protein,low fat set yoghurt

The effects of casein micelle size on rheological properties of high protein (5.6% crude protein), low fat (≤0.2%) set yoghurt were investigated. Microfiltration with 0.20 μm membranes was used to fractionate skim milk with an average casein micelle size of ∼174 nm into a retentate and a permeate containing “large” (∼183 nm) and “small” (∼129 nm) casein micelles, respectively. The permeate containing the small casein micelles was further concentrated with 0.10 μm membranes. Yoghurt milk bases with large or small casein micelles were subjected to heat treatment at two different temperatures; 95 °C or 75 °C for 5 min. Yoghurt milk base with small casein micelles gave set yoghurts with higher storage modulus (G′) and higher firmness than yoghurt milk base with large casein micelles. Increased gelation capacity can be attributed to an increased amount of κ-casein in the yoghurt milk base containing small casein micelles.     

Effects of goat cheese on Helicobacter pylori activity and gastrointestinal complaints

To investigate whether and how consumption of goats' milk cheese affects Helicobacter pylori activity in the stomach of infected subjects, a randomized, controlled and blind study was performed. Sixty volunteers consumed 4 × 25 g day⁻¹ “Gouda-type” cheese for 3 weeks, prepared from either goats' or cows' milk. The goats' milk cheese was rich in short- and medium-chain fatty acids. Immediately before the start and thereafter every seven days, H. pylori activity was measured by the ¹³C-urea breath test, and gastrointestinal well-being was recorded weekly by validated questionnaires. Neither goats' nor cows' milk cheese had any significant effect on H. pylori activity. Ingestion of both cheeses improved gastrointestinal well-being but had no effect on stool parameters. The difference of the total symptoms score was significant between day 0 and 21 in each dietary groups, but not between the goats' and cows' milk cheese.     

藜麦酸奶工艺及其品质研究

以藜麦浆、全脂奶粉为主要原料,研究了藜麦酸奶加工工艺,通过单因素和正交试验确定藜麦酸奶的最佳工艺条件,并利用固相微萃取-气相色谱-质谱联用法（SPME-GC-MS）分析藜麦酸奶的挥发性风味成分。结果表明,藜麦酸奶的最佳工艺条件为：藜麦浆料水比1∶5（g∶mL）,藜麦浆添加量20%,白砂糖添加量7%,乳酸菌接种量0.3%,发酵温度40 ℃及发酵时间7 h。在此工艺条件下所制得藜麦酸奶蛋白质含量为3.18 g/100 g,pH值为4.35,酸度为84.00 °T,感官评分为90分。SPME-GC-MS分析共检出藜麦酸奶中挥发性化合物35种,主要包括酯类、酸类、酮类、醛类等,其中己二酸二乙基己基酯含量最大,为71.71%。     

GC-MS metabolomics comparison of yoghurts from sheep's and goats' milk

In this study, the polar metabolite profile of commercial yoghurt samples produced in Sardinia (Italy) from milk of local sheep and goats was studied by GC-MS and multivariate statistical data analysis (MVA). Milks underwent the same manufacturing procedures and yoghurts were analysed one day post-manufacture. Results of discriminant analysis indicated that the two yoghurt types had very different metabolite profiles, with different levels of health promoting compounds. Goats' milk yoghurt was richer in free amino acids, γ-aminobutyric acid, pyroglutamic acid and β-phenyllactic acid when compared with yoghurt produced with sheep's milk. Sheep's milk yoghurt was characterised by higher levels of myo-inositol, N-acetylgalactosamine and N-acetylglucosamine. Comparing yoghurt metabolites with those of the original milk, it was found that goats' milk underwent stronger metabolite changes after inoculum. The comparison between the two yoghurt types gave us a deeper insight on the effects of manufacture on different milks.     

Transglutaminase cross-linking of milk proteins and impact on yoghurt gel properties

A novel yoghurt process was investigated in which milk proteins were covalently cross-linked by a microbial transglutaminase (TG) preparation containing glutathione (TG+GSH). As unheated milk is normally less reactive towards TG, TG+GSH was applied to enable non-inhibited cross-linking without requiring a pre-heat treatment beyond pasteurisation conditions. After the TG+GSH incubation phase, the enzyme was inactivated by heat treatment of the yoghurt milk prior to fermentation. During yoghurt fermentation, no negative effect of TG+GSH on fermentation time was found. Protein cross-linking by TG+GSH was enhanced, resulting in higher apparent viscosity and a higher degree of protein polymerisation than that given by TG without GSH. Furthermore, different ratios of casein to whey proteins (CWP ratios) were used to investigate the effect of both protein fractions on covalently cross-linked yoghurt gel structures. The results showed a relationship between extent of cross-linking, apparent viscosity and CWP ratio of the yoghurt gels. During storage for up to 6 weeks at 4 °C, no changes in rheological properties and degree of protein polymerisation were measurable for stirred yoghurt gels prepared from cross-linked milk proteins.     

The quality of set‐style yoghurt responsible to partial lactose hydrolysis followed by protein cross‐linking of the skimmed milk

Skimmed milk used for set‐style yoghurt production was treated with lactase at 0.1 g/kg for 30 min to give partial lactose hydrolysis and then treated with horseradish peroxidase and glucose oxidase at 200 and 6 kU/kg protein to result in protein cross‐linking. Two treatments conferred higher apparent viscosity on the milk, but led to the yoghurt prepared from it with insignificantly different chemical compositions to the counterparts (P > 0.05). The prepared yoghurt also showed decreased syneresis (about 17.7%), higher apparent viscosity and viscoelastic modulus, firmer texture and finer microstructure. This ternary enzyme system is a potential approach to improving the quality of set‐style yoghurt.     

Development of made‐in‐transit set culture yoghurt: effect of increasing the concentration of reconstituted skim milk as the milk base

The fermentation time, yoghurt acidity expressed as lactic acid, starter culture growth, viscosity and firmness of made‐in‐transit (MIT) set culture yoghurt produced using different concentrations of reconstituted skim milk powder (SMP) from 12% to 20% (w/v) as the milk base were investigated. All milk base formulations were ultra‐high temperature sterilised at 138 °C for 6 s. The results revealed that increasing the SMP concentration increased the viscosity and firmness of MIT set culture yoghurt. At 20% SMP, viscosity and firmness were 4650.8 cP and 1.266 N, respectively. Fermentation of MIT set culture yoghurt with 20% SMP was observed to be faster than with the other conditions. The fermentation time for a medium containing from 14% to 20% SMP could be extended to 168 h, reaching a final pH of 4.50–4.37 and at the same time improving the texture of the MIT set culture yoghurt. The SMP concentration had no influence on the total viable counts of starter bacteria in the yoghurt. The texture of MIT set culture yoghurt may be improved by increasing the concentration of SMP.     

Influence of enrofloxacin on the coagulation time and the quality parameters of goat's milk yoghurt

Three batches of yoghurts were made from goat's milk with different enrofloxacin concentrations (0, 50, 100 and 150 μg/kg). Quality parameters were analysed at 1, 7, 14 and 28 days at 5 °C. Drug residues were also quantified by HPLC. Coagulation time and most yoghurt properties remained unaffected by the presence of enrofloxacin in goat's milk. However, quality parameters were affected by the storage period. 74.9–99.2% of enrofloxacin initially added to goat's milk remained in the yoghurt throughout its entire shelf life, potentially posing a risk to consumer health. Therefore, an enrofloxacin maximum residue limit in yoghurt should be established.     

Evaluation of total phenol content and antioxidant properties of encapsulated grape seed extract in yoghurt

The effect of encapsulated (En) and nonencapsulated (NE) grape seed extract (GSE) at 1% level added to milk before its fermentation was evaluated on the physicochemical properties, total phenolic content and antioxidant activity of the resulting yoghurt. Encapsulated GSE resulted in a product comparable to the control, based on sensory properties, acidity, water‐holding capacity, viscosity and colour, along with a threefold increase in total phenolic content and fourfold increase in antioxidant activity. The GSE addition resulted in no effect on the viability of Streptococcus thermophilus and Lactobacillus bulgaricus subsp. delbrueckii counts. The product with NE‐GSE had poor sensory properties and lesser polyphenol stability during storage as compared to En‐GSE yoghurt.     

Volatile organic compound profiles of yoghurt produced from cow's milk with different somatic cell counts

The present study aimed to investigate the effect of somatic cell count (SCC) of raw cow's milk on the volatile organic compound (VOC) profiles of yoghurt. Test yoghurt samples were produced from three batches of cow's milk with low, medium and high SCC, respectively. The VOCs were determined by gas chromatography–mass spectrometry (GC–MS) analysis. A lower diacetyl and acetoin content and a higher content of 2‐heptanone, and butanoic and hexanoic acids were established in the yoghurt samples from batches with high SCC of above 1 000 000 cells/cm³. The increased SCC of cow's milk had a negative effect on the volatile organic compound profiles of yoghurt.     

Physical properties and microstructure of yoghurts supplemented with milk protein hydrolysates

The physical properties and the microstructure of yoghurts containing probiotic bacteria, and supplemented with milk protein hydrolysates, were studied. Three casein hydrolysates and three whey protein hydrolysates were added to milk at a concentration ranging from 0.25 to 4 g L⁻¹. The milks were then fermented with either of two different cultures. The resulting yoghurts with added hydrolysates were compared to the control yoghurt without supplementation. For both cultures, addition of hydrolysates decreased the complex viscosity and graininess in yoghurts. The addition of hydrolysates also reduced fermentation time. Microstructural observations showed a more open and less branched structure in yoghurts when milk protein hydrolysates were incorporated. The difference in fermentation time between milks with different levels of added hydrolysates could partially explain the differences in microstructure and physical properties of the final yoghurts.     

Modifying the microstructure of low-fat yoghurt by microfluidisation of milk at different pressures to enhance rheological and sensory properties

The effects of microfluidisation of milk at different pressures, prior to heat treatment, on structural and sensory properties of low-fat stirred yoghurt, were investigated. Low-fat yoghurts prepared from microfluidised milk were compared with low-fat (1.5%) and full-fat (3.5%) control yoghurts made with homogenised (20/5 MPa) milk. The microstructure of low-fat yoghurts prepared with microfluidised milk consisted of smaller and more uniform fat globules, well incorporated into more interconnected fat-protein gel networks, compared with those of control yoghurts. This modification in microstructure caused significant changes in gel particle size, sensory profile and rheological behaviour. Microfluidisation increased the gel particle size, gel strength and viscosity; marked beneficial effects were found at higher pressures (50–150 MPa). Microfluidising milk at 50–150 MPa increased the gel strength by 171–195% and viscosity by 98–103%, creating low-fat yoghurts with creaminess and desirable texture properties similar to, or better than, full-fat conventional yoghurt.     

花生芽鹰嘴豆复合酸奶的发酵工艺优化

以奶粉、花生芽和鹰嘴豆为主要原料,安琪12菌型酸奶发酵剂为发酵菌种,制备花生芽鹰嘴豆复合酸奶。以酸度、黏度、乳酸菌数、感官评分为评价指标,研究糖添加量、接种量、发酵温度和发酵时间对花生芽鹰嘴豆复合酸奶发酵的影响,并采用正交试验优化其发酵条件。结果表明,各因素对酸奶感官评分的影响顺序依次为接种量>糖添加量>发酵温度>发酵时间;各因素对乳酸菌数的影响依次为接种量、发酵时间、发酵温度、糖添加量。花生芽鹰嘴豆复合酸奶最佳发酵工艺条件为接种量5 g/L,白砂糖添加量8%,发酵温度39℃,发酵时间24 h。此优化条件下获得的酸奶风味良好,乳酸菌数为8.11×108CFU/m L,感官评分为92分,酸度为78.31°T。     

Viability of Lactobacillus acidophilus in rice bran‐enriched stirred yoghurt and the physicochemical and sensory characteristics of product during refrigerated storage

This study was aimed at investigating the fortification of probiotic yoghurt with rice bran to increase nutritional properties of the product. The different levels of rice bran (0.3%, 0.6%, 0.9% and 1.2%) were incorporated into milk. The yoghurt samples were produced after pasteurisation, addition of starter culture and 1% Lactobacillus acidophilus suspension (6 × 10⁸ CFU mL^?1) and incubation. During sample storage in refrigerator, the viability of L. acidophilus, viscosity and physicochemical and sensory properties of product were investigated. Rice bran significantly increased the viability of L. acidophilus (P < 0.05). In addition, all probiotic yoghurts incorporating rice bran indicated higher viscosity and acidity and lower pH and syneresis compared to plain yoghurts. Furthermore, increments in rice bran incorporation levels resulted in a reduction in consumers' sample preferences. In general, the addition of rice bran at a suitable level could increase L. acidophilus viability and improve quality attributes of yoghurt.     

Acid-induced gelation of whey protein polymers: effects of pH and calcium concentration during polymerization

Heating whey protein dispersions (90°C for 15 min) at low ionic strength and pH values far from isoelectric point (pH>6.5) induced the formation of soluble polymers. The effect of mineral environment during heating on the hydrodynamic characteristics and acid-induced gelation properties of polymers was studied. Whey protein dispersions (80 g/l) were denatured at different pH (6.5–8.5) and calcium concentrations (0–4 mm) according to a factorial design. At pH 6.5, the hydrodynamic radius of protein polymers increased with increasing calcium concentration, while the opposite trend was observed at pH 8.5. Intrinsic viscosity results suggested that heating conditions altered the shape of protein polymers. Whey protein polymers were acidified to pH 4.6 with glucono-δ-lactone and formed opaque particulate gels. The storage modulus and firmness of gels were both affected by conditions used to prepare protein polymers. As a general trend, polymers with high intrinsic viscosity produced stronger gels, suggesting a relationship between polymer shape and gel strength.Acid gelation properties of whey protein polymers makes them suitable ingredients for yoghurt applications. Using whey protein polymers to standardize protein content increased yoghurt viscosity to 813 Pa.s while using skim milk powder at same protein concentration increased yoghurt viscosity to 393 Pa.s. Water holding capacity of protein polymers in yoghurt was 19.8 ml/g compared to 7.2 ml/g for skim milk powder protein. Acid gelation properties of whey protein polymers are modulated by calcium concentration and heating pH and offers new alternatives to control the texture of fermented dairy products.     

Evaluation of the effect of fennel (Foeniculum vulgare Mill) essential oil addition on the quality parameters and shelf‐life prediction of yoghurt

Yoghurt was prepared by adding three concentrations of fennel essential oil (FEO) (2.5, 5 and 7.5 µL) in 100 mL of pasteurised milk. Fennel essential oil did not affect the viability of yoghurt starters during fermentation. Based on sensory analysis, only the 5‐µL FEO concentration was incorporated in order to investigate the physicochemical and microbiological properties of enriched yoghurt during storage. Results showed that FEO in yoghurt did not significantly affect the quality after acidification (P > 0.05). However, total solid content, syneresis and lightness (L*) differed significantly (P < 0.05). Bacterial counts indicated that the control yoghurt had the highest values. Fortified yoghurt had an increased shelf life of 29 days.     

Properties of set-style skim milk yoghurt as affected by an enzymatic or Maillard reaction induced milk protein oligomerisation

Protein oligomers (2.9 × 10⁴-3.0 × 10⁵ g/mol) were introduced into yoghurt in amounts of 15-37% of the total protein by an enzymatic modification of proteins in yoghurt milk by lactoperoxidase, laccase or glucose oxidase as well as by a dry matter increase of yoghurt milk with sodium caseinate/lactose, sodium caseinate/pectin and total milk protein/lactose Maillard products. Yoghurt from enzymatically treated milk was characterised by an up to 10% lower acidity, up to 47% diminished gel strength and up to 18% decreased whey drainage than yoghurt from untreated milk. Yoghurt from protein/saccharide Maillard product enriched milk exhibited up to 4% reduced acidity, up to 27% increased acetic aldehyde content as well as up to 58% decreased whey drainage in relation to yoghurt from untreated protein/saccharide mixture enriched milk. Sensorically, yoghurt from enzymatically treated milk as well as from protein/saccharide Maillard product enriched milk was described by an even and whey-draining appearance, by a soft, homogeneous and creamy consistency as well as by a mild, less yoghurt characteristic taste and smell.This study for the first time presents an overview over the impact of novel protein oligomerisation techniques on physicochemical and sensory properties of yoghurt in regard to possible practical applications of an enzymatic as well as Maillard reaction induced oligomerisation in complex food systems.     

酸豆乳发酵工艺条件的优化

以新鲜大豆和成品牛乳为原料,研究了发酵工艺对酸豆乳酸度、黏度和乳酸菌活力等指标的影响。结果显示,以传统酸奶发酵剂乳酸菌为菌种,大豆浆液为主要原料,经发酵获得酸豆乳工艺可行。在单因素实验的基础上,经正交实验确定酸豆乳发酵的最佳工艺条件为:豆浆和牛奶体积比为5∶5,发酵9 h,按0.5 g/L发酵液添加驯化后乳酸菌液作为发酵剂,经发酵得到的产品酸度达到70°T以上,黏度2025 mPa.s,凝乳性较好,美兰褪色时间为50 min,乳酸菌活力提高,无豆腥味。