Novel bacteriocinogenic Enterococcus hirae and Pediococcus pentosaceus strains with antilisterial activity isolated from Brazilian artisanal cheese

We isolated and characterized bacteriocin producers Enterococcus hirae ST57ACC and Pediococcus pentosaceus ST65ACC from raw milk artisanal cheeses. Their bacteriocins were tolerant to temperatures from 4°C to 100°C and under sterilization conditions (121°C for 15 min). Additionally, the tested bacteriocins remained active after being exposed to pH 2.0 to 10.0 for 2 h. The activity of the bacteriocins was affected by proteolytic enzymes but remained stable after treatment with EDTA, sodium dodecyl sulfate, NaCl, skim milk, and Tween 80. Cell-free supernatants were capable of inhibiting Listeria innocua and several strains of Listeria monocytogenes obtained from different sources and belonging to different serotypes. When L. monocytogenes 211 and L. monocytogenes 422 were treated with bacteriocins, growth was completely inhibited over 12 h. Cocultures of bacteriocinogenic strains and L. monocytogenes 422 in skim milk showed that E. hirae ST57ACC could control the growth of the pathogen in the matrix after 48 h. None of the selected isolates presented positive results on a screening panel for 25 bacteriocin-related genes, however, indicating that both strains might express novel bacteriocins.     

浓缩酪蛋白胶束成分的影响因素及其在奶酪生产中的应用

目前,采用膜过滤技术可从脱脂奶中分离酪蛋白,随后通过浓缩、杀菌、干燥等工艺获得浓缩酪蛋白胶束。对浓缩酪蛋白胶束成分的影响因素及其在奶酪生产中的应用进行综述,发现膜过滤期间的pH值、温度和洗滤条件均会影响浓缩酪蛋白胶束的成分,使其具有不同浓度的酪蛋白、乳清蛋白、乳糖以及钙。而且可以利用浓缩酪蛋白胶束标准化原奶,从而制备成分和品质一致的奶酪;也可以利用不同成分的浓缩酪蛋白胶束获得不同的原奶组合物,从而制备所需品质和功能的奶酪。总之,在奶酪生产过程中添加浓缩酪蛋白胶束能够影响奶酪的成分、质地以及风味等,但通过调整膜过滤和奶酪生产的工艺参数可以解决这些问题。未来还需获得一种经济有效的方式来保存浓缩酪蛋白胶束,赋予其更长的保质期,良好的凝乳酶凝乳特性,从而保证奶酪的品质和产量。     

Free and immobilized Lactobacillus casei ATCC 393 on whey protein as starter cultures for probiotic Feta-type cheese production

The use of free and immobilized Lactobacillus casei ATCC 393 on whey protein as starter culture in probiotic Feta-type cheese production was evaluated. The probiotic cultures resulted in significantly higher acidity; lower pH; reduced counts of coliforms, enterobacteria, and staphylococci; and improved quality characteristics compared with cheese with no culture. Microbiological and strain-specific multiplex PCR analysis showed that both free and immobilized L. casei ATCC 393 were detected in the novel products at levels required for conferring a probiotic effect at the end of the ripening. The effect of starter culture on production of volatile compounds was investigated by the solid-phase microextraction gas chromatography-mass spectrometry analysis technique. The immobilized cells resulted in an improved profile of aroma-related compounds and the overall high quality of the novel products was ascertained by the preliminary sensory test. Finally, the high added value produced by exploitation of whey, which is an extremely polluting industrial waste, was highlighted and assessed.     

Sensory analysis and species-specific PCR detect bovine milk adulteration of frescal (fresh) goat cheese

The Brazilian market for dairy products made from goat milk is increasing despite the seasonality of production and naturally small milk production per animal, factors that result in high-priced products and encourage fraud. In Brazil, no official analytical method exists for detecting adulteration of goat dairy products with cow milk. The aim of this study was to design a strategy to investigate the adulteration of frescal (fresh) goat cheeses available in the Rio de Janeiro retail market, combining analysis of cheese composition and the perception of adulteration by consumers. Commercial goat cheeses were tested by using a duplex PCR assay previously designed to authenticate cheeses, by targeting the mitochondrial 12S ribosomal RNA genes of both species simultaneously. The PCR test was able to detect 0.5% (vol/vol) cow milk added during goat cheese formulation. The analysis of 20 locally produced goat cheeses (20 lots of 4 brands) showed that all were adulterated with cow milk, even though the labels did not indicate the addition of cow milk. To estimate the ability of consumers to perceive the fraudulent addition of cow milk, a triangle test was performed, in which cheeses formulated with several different proportions of goat and cow milk were offered to 102 regular consumers of cheese. Detection threshold analysis indicated that almost half of the consumers were able to perceive adulteration at 10% (vol/vol) cow milk. Effective actions must be implemented to regulate the market for goat dairy products in Brazil, considering the rights and choices of consumers with respect to their particular requirements for diet and health, preference, and cost.     

Characterization of Siahmazgi cheese,an Iranian ewe's milk variety: Assessment of physico-chemical,textural and rheological specifications during ripening

Siahmazgi cheese is an Iranian locally-made cheese produced from ewe's milk or a mixture of ewe and goat's milks in the suburbs of Rasht in the north of Iran. This kind of cheese is kept in sheepskin for six months under special condition which cause distinct physicochemical and textural characteristics. Therefore, in the present study the effect of ripening time (6 months) on the chemical, physicochemical, rheological and textural characteristics of Siahmazgi cheese (18 samples) was investigated. The rheological and textural properties were determined using rheometer (frequency sweep) and texture analyzer (uniaxial compression). Based on our findings, the measured values including pH, titratable acidity (TA), dry matter, fat, protein, ash, salt content, water soluble nitrogen in total nitrogen, and non-protein-nitrogen in total nitrogen significantly increased during ripening (P < 0.05). Furthermore, the results showed that the six-month ripened Siahmazgi cheese contained high values of dry matter (59.95 ± 0.08 g/100 g), salt (5.65 ± 0.05 g/100 g), and ash (7.24 ± 0.02 g/100 g). Regarding rheological and textural properties, storage modulus (G′), loss modulus (G″), fracture stress (σ_f) and firmness increased while loss tangent and fracture strain decreased.     

Commercial application of high-pressure processing for increasing starter-free fresh cheese shelf-life

Different non-thermal technologies have been proposed to extend the shelf-life of solid food products, high-pressure processing (HPP) being one of the emerging technologies which has been most extensively studied. In this study, one of the first commercial industrial-scale applications of HPP on a starter-free fresh cheese, with the aim of increasing its shelf-life, is presented. The effect of 500 MPa (5 min, 16 °C) on physico-chemical, microbial, colour, microstructure, texture and sensorial characteristics of starter-free fresh cheeses during cold storage of 21 days was studied. The results showed that pressurised cheeses presented a shelf-life of about 19–21 days when stored at 4 °C, whereas control cheese became unsuitable for consumption on day 7–8. On the other hand, cheese treated at 500 MPa was firmer and more yellow than the untreated one. However, these changes, which were detected by instrumental and sensory analysis, did not affect the preference for pressurised cheese. These results may lead to practical applications of HPP in the food industry to produce microbiologically safe cheese with extended shelf-life and sensory quality.     

Quantitative detection of Listeria monocytogenes in raw milk and soft cheeses: Culture-independent versus liquid- and solid-based culture-dependent real time PCR approaches

A culture-independent and two culture-dependent real time (rt-) PCR approaches were developed to quantitatively identify Listeria monocytogenes in raw milk and soft cheeses. The optimised rt-PCR revealed 100% inclusivity and exclusivity. DNA- and cell-based standard curves showed a good linearity of response (R² ≥ 0.987 and R² ≥ 0.998, respectively) for five orders of magnitude (39 × 10⁵ – 3 × 10⁰ genome equivalents and 10⁶–10¹ CFU equivalents, respectively) with about 100% relative accuracy and inter-assay variability ≤0.90%. Up to 1 genome equivalent/and 10 CFU/reaction were quantified in the DNA and cell standard curves, respectively. The rt-PCR was then combined with a liquid- (MPN technique) or a solid- (ALOA and PALCAM) based enumeration. The diagnostic sensitivity of the different approaches was investigated in artificially contaminated raw milk and soft cheeses. The rt-PCR culture-independent approach performed well in raw milk and (with a lower sensitivity) in stracchino cheese-based standard curves. MPN/rt-PCR was the best approach to enumerate low levels of L. monocytogenes in raw milk and stracchino cheese, while the ALOA-based rt-PCR quantification was more effective than the PALCAM-based. These performances were confirmed when 23 real samples of raw milk and soft cheeses by both the rt-PCR approaches were assayed.     

Effects of tropical fruit pulps and partially hydrolysed galactomannan from Caesalpinia pulcherrima seeds on the dietary fibre content,probiotic viability,texture and sensory features of goat dairy beverages

The use of cheese whey and probiotic cultures in the production of dairy beverages has been highly attractive; nonetheless, whey-based goat beverages tend to be poor and watery when compared to fermented milks. The addition of fruits and fibre ingredients might improve texture and mouthfeel of this kind of product. Fermented whey-based goat beverages prepared using Streptococcus thermophilus TA-40 as starter culture, with added guava or soursop pulps, and with or without addition of partially hydrolysed galactomannan from Caesalpinia pulcherrima seeds (PHGM), showed to be good vehicles for Bifidobacterium animalis subsp. lactis BB-12 and Lactobacillus rhamnosus Lr-32, maintaining their viability above 7 log CFU/ml during 21 days. PHGM increased the dietary fibre content and enhanced the instrumental texture and sensory features of both guava and soursop dairy beverages, especially texture, appearance, and overall acceptability. The PHGM might be recommended to improve nutritional and sensory quality of fermented probiotic beverages produced with goat milk and cheese whey.     

不同乳酸菌对低脂Mozzarella干酪品质的影响

研究不同乳酸菌对低脂Mozzarella干酪品质的影响。采用无盐渍新工艺制作低脂Mozzarella干酪,经测定干酪的脂肪含量为9.85%。通过测定可溶性氮的指标、未融化干酪的质构特性、融化干酪的融化性和感官评定等对其进行研究。结果表明：低脂组的质构、融化性和风味均低于全脂组,但唾液链球菌嗜热亚种（ST）＋德氏乳杆菌保加利亚亚种（LB）＋干酪乳杆菌（LC）3 种乳酸菌组合制作的低脂Mozzarella干酪质构、融化性和风味等指标最接近全脂组。与生产Mozzarella干酪所用的传统乳酸菌组合（ST＋LB）相比,ST＋LB＋LC 3 种乳酸菌的组合,能有效地改善低脂Mozzarella干酪硬度大、融化性小、风味差的缺陷。