Quality and microbial stability of partially baked bread during refrigerated storage

Partially baked bread was prepared and stored at 1 °C or 7 °C for 28 days. Periodically, this product was subjected to moisture, hardness, and microbiological analyses. After storage, the baking process of part-baked bread was completed and product evaluated according to microbiological, physical, and sensorial tests, as well as hardness analysis. Part-baked breads stored at 7 °C showed mold growth at day ninth, while the product stored at 1 °C did not show mold growth through 28 days. The full-baked bread obtained from part-baked samples stored at 1 °C showed higher values of hardness and change in crumb hardness, and lower sensorial quality than bread from part-baked samples stored at 7 °C. Moisture content, specific volume, and width/height ratio in the full-baked bread were not affected by storage time and temperature.     

Changes in the microbiological and chemical characteristics of an artisanal, low-fat cheese made from raw ovine milk during ripening

Changes in the microbial flora of batzos cheese made from raw ovine milk were studied during ripening. Lactic acid bacteria and Enterobacteriaceae were the predominant groups of micro-organisms. Cheeses manufactured in summer had higher microbial counts than those made in spring, with the exception of staphylococci. Nevertheless, Enterobacteriaceae and coliforms decreased more rapidly in cheese made in summer and counts at the end of storage were lower than those in spring cheese.
Enterococci predominated in the ripened curd of cheese made in spring, whereas lactobacilli were the most abundant lactic acid bacteria in cheese made in summer. Enterococcus faecium was the predominant species in spring, and Lactobacillus paracasei ssp. paracasei predominated in cheese made in summer. The pH of the cheeses was > 5.0 throughout ripening, and NaCl-in-moisture content (> 8.0%) permitted the growth and survival of salt-tolerant micro-organisms. α_s1-Casein degraded at a faster rate than β-casein; both caseins were hydrolysed more rapidly in spring than in summer. The free amino acid content became higher in summer cheese (566.24–3460.25 µg/g of glycine equivalent) than in spring cheese because of the progress of ripening. Moreover, the milk fat of the cheese was degraded more in the summer than in the spring. The results suggest that there could be advantages to using starter cultures and improving the level of hygiene during milk and cheese production in order to eliminate undesirable micro-organisms and standardize cheese quality.     

不同贮存条件对原料乳质量的影响

研究了原料乳质量和贮存温度及贮存时间之间的关系.通过菌落总数的检测和酸度的测定,探讨了不同贮存温度随时间对原料乳中菌落总数和酸度的影响,旨在为优质原料乳的贮运提供参考.结果表明,在4℃贮存条件下,原料乳存放36 h,对质量没有较大的影响;在原料乳温度达到10～15℃的时候,存放时间不宜超过12 h.     

Biogenic amine changes in barramundi (Lates calcarifer) slices stored at 0 °C and 4 °C

The biogenic amines formation in barramundi (Lates calcarifer) slices kept for 15 days at 0 °C and 4 °C were investigated using nine biogenic amines, total plate counts and biogenic amines formers. Significant differences in biogenic amines concentrations of barramundi slices stored at 4 °C and at 0 °C after 3 days of storage were observed. All amines, except tryptamine, 2-phenylethylamine, tyramine and agmatine in the slices increased with time during storage at both temperatures. At the end of the storage period, histamine concentrations were 82 mg/kg and 275 mg/kg for samples kept at 0 °C and 4 °C, respectively. At day 15, the total plate count was approximately 8.6 log CFU/g for sample kept at 0 °C and 9.7 log CFU/g for samples kept at 4 °C. Histamine-forming bacteria (HFB) in all samples ranged from 5.4 to 6.1 log CFU/g at 0 °C and 4 °C, respectively. The observed shelf-life of barramundi slices were 6–9 days.     

Effect of various storage conditions on the stability of quinolones in raw milk

Research on the storage stability of antibiotic residues in milk is important for method development or validation, milk quality control and risk assessment during screening, confirmation, qualitative or quantitative analysis. This study was conducted using UPLC-MS/MS to determine the stability of six quinolones – ciprofloxacin (CIP), danofloxacin (DAN), enrofloxacin (ENR), sarafloxacin (SAR), difloxacin (DIF) and flumequine (FLU) – in raw milk stored under various conditions to investigate if quinolones degrade during storage of milk, and finally to determine optimal storage conditions for analysis and scientific risk assessment of quinolone residues in raw milk. The storage conditions included different temperatures and durations (4°C for 4, 8, 24 and 48 h; –20°C for 1, 7 and 30 days; –80°C for 1, 7 and 30 days), thawing temperatures (25, 40 and 60°C), freeze–thaw cycles (1–5), and the addition of different preservatives (sodium thiocyanate, sodium azide, potassium dichromate, bronopol and methanal). Most quinolones exhibited high stability at 4°C for up to 24 h, but began to degrade after 48 h. In addition, no degradation of quinolones was seen when milk samples were stored at –20°C for up to 7 days; however, 30 days of storage at –20°C resulted in a small amount of degradation (about 30%). Similar results were seen when samples were stored at –80°C. Moreover, no losses were observed when frozen milk samples were thawed at 25, 40 or 60°C. All the quinolones of interest, except sarafloxacin, were stable when milk samples were thawed at 40°C once and three times, but unstable after five freeze–thaw cycles. Preservatives affected the stability of quinolones, but the effects differed depending on the preservative and quinolone. The results of this study indicate optimum storage protocols for milk samples, so that residue levels reflect those at the time of initial sample analysis, and should improve surveillance programmes for quinolones in raw milk.     

屋顶奶贮藏期品质变化的研究

研究了市售屋顶型纸盒包装纯鲜牛奶（以下简称“屋顶奶”）开封后在不同温度下（0、4、7℃）贮藏过程中微生物、脂肪质量分数和滴定酸度等指标的变化。结果表明,在不同的贮藏温度下，微生物数量在开始的5d内变化不大，到贮藏后5d则不断增加；脂肪质量分数在起始的2～3d内基本稳定，随后几天逐渐下降；酸度在起始的3则内出现下降趋势，在随后的3～5d出现波动，接着又出现回升。总之，随着贮藏温度的升高，屋顶奶品质变化进程加快，但在贮藏期内以上指标均达到质量标准。     

低温储存期间原料乳微生物预测模型建立

本研究对秋季低温储存原料乳进行预测微生物学研究。使用Gompertz模型建立4~14℃储存的秋季原料乳中总菌落和嗜冷菌的生长动力模型。模型可以有效的模拟秋季原料乳中微生物的生长情况,模型的相关系数均大于0.972,可以用来预测微生物生长情况和达到控制下限的时间。研究表明嗜冷菌是低温储存的原料乳中优势微生物,在4~8℃储存温度下总菌落数与嗜冷菌的数量呈很好的相关性(R~2=0.931),可以通过总菌数推算出嗜冷菌的数量,保证乳制品的品质。      

生产贮藏条件对原料奶中微生物的影响

以手工挤奶条件下不同来源的原料奶为研究对象,在冷藏(4℃)、室温(19℃)条件下,分别贮藏0,3,6,9 h后检测原料奶中菌落总数(TBC)、芽孢总数(TSC)、耐热芽孢数、嗜冷菌总数。结果表明,随着贮藏温度增加、时间延长,原料奶中微生物增幅加快(P<0.05),冷链条件下(4℃)贮运原料奶对控制微生物生长繁殖具有重要作用。手工挤奶条件下室温(19℃)贮奶3h、冷藏(4℃)贮奶6h后原料奶中菌落总数超过5×105 mL-1的国家标准,原料奶的芽孢总数、耐热芽孢数和嗜冷菌数均超出液态奶的生产要求,特别不利于长效奶(保质期30 d以上)的生产。改善牛奶生产环境对提高原料奶品质具有重要的作用。     

Strategies for raw sheep milk storage in smallholdings: Effect of freezing or long-term refrigerated storage on microbial growth

We assessed the effects of freezing and refrigeration over long periods on the microbiological quality of sheep milk. The raw milk was frozen in 1-L plastic bags or 5-L milk buckets and, after 1 mo, thawed at 7 or 25°C. We evaluated these samples immediately after thawing (d 0) and after 1 d of storage at 7°C. Furthermore, we stored fresh raw milk at 7°C for 10 d in the same packages and in a bulk milk cooler at 4°C (adding 10% of fresh raw milk daily). The total bacterial, total psychrotolerant, and proteolytic psychrotolerant counts were evaluated before and after thawing (for previously frozen milk) and daily (for refrigerated milk). The frozen-thawed milks showed no significant increase in bacterial counts immediately after thawing for all samples (<0.7 log cfu/mL), but only the samples packaged in 1-L bags and thawed at 7°C remained microbiologically adequate after 1 d of storage. Findings of the refrigerated samples were modeled using a modified Gompertz equation, obtaining a lag phase of around 0.5 (5-L bucket), 2.6 (1-L bag), and 7.0 (bulk milk cooler) d for total bacterial and total psychrotolerant counts. Maximum growth rates (µ_max) were 1.0 and 1.0 (5-L bucket), 1.2 and 1.3 (1-L bag) and 3.0 and 1.5 (bulk milk cooler) ln(cfu/mL) per day for total bacteria and total psychrotolerant counts, respectively. Compared with total bacteria and total psychrotolerant bacteria, psychrotolerant proteolytic bacteria grew slowly, reaching unacceptable counts only after 9 to 10 d of storage. The studied methods are interesting alternatives for preserving raw sheep milk on smallholdings.     

Survey of the occurrence of Aflatoxin M1 in ovine milk by HPLC and its confirmation by MS

During the period of October-July 2000, 240 samples of dairy ewes milk, obtained from farms of Enna (Sicily, Italy), were checked for Aflatoxin M(1) (AFM(1)) by HPLC using a fluorimetric detector. The limit of detection and the limit of quantification were 250 ng/L for AFM(1). All the positive milk samples for AFM(1) were confirmed by LC-MS. AFM(1) was detected in 81% of milk samples, ranging from 2 to 108 ng/L. Three samples were over the legal limits (50 ng/L). Mean contamination of samples obtained from stabulated ewes was higher than that from grazing ewes (35.27 vs. 12.47 ng/L). Furthermore, samples collected in the period September-October showed higher contamination than samples collected during the other months (42.68 vs. 10.55 ng/L). Both differences are related to the administration of compound feed. Based on current toxicological knowledge we concluded that the AFM(1) contamination levels recorded in ewe milk did not present a serious human health hazard. However, as ewe milk is exclusively used to produce cheese due to its higher protein content, and also considering the preferential binding of AFM(1) to casein during coagulation of milk, a potentially high concentration effect could occur, thus the surveillance of contamination levels should be more continuous and widespread.     

The effect of dietary oregano essential oil on microbial growth of rabbit carcasses during refrigerated storage

The effect of dietary supplementation with oregano essential oil on microbial growth of rabbit carcasses during refrigerated storage was investigated. A total of 45 weaned rabbits were separated into three equal groups with three subgroups each. One group was given the basal diet and served as control and the other two groups were administered diets supplemented with oregano essential oil at levels of 100 and 200 mg/kg diet, respectively (OR100 and OR200 groups). Total viable counts, Pseudomonas spp., lactic acid bacteria, Brochothrix thermosphacta, Enterobacteriaceae and yeast and mould counts, as well as off-odours and appearance of slime were all assessed on rabbit carcasses stored at 3 ± 1 °C for 12 days. The results showed that performance parameters were not affected (p > 0.05) whereas the dietary supplementation with oregano essential oil resulted in lower (p < 0.05) average microbial counts on the carcasses, compared to controls, throughout storage. Dietary supplementation with oregano essential oil at 200 mg/kg was more effective in inhibiting microbial growth compared with 100 mg/kg. Sensory evaluation scores indicated that the carcasses obtained from OR100 and OR200 groups gave a noticeable putrid odour after days 8 and 10, respectively, whereas the control carcasses developed off-odours after the 6th day of storage. Slime formation in the controls was observed after day 6, while the OR100 and OR200 groups were just beginning to show slime after days 8 and 10, respectively.     

Controlling psychrotrophic bacteria in raw buffalo milk preserved at 4 °C with esterified legume proteins

The activity of native and esterified legume proteins in controlling the growth of psychrotrophic bacteria contaminating raw buffalo milk kept at 4 °C as well as milk quality was followed and assessed. Supplementation of milk samples with 0.5% of methylated legume proteins has considerably reduced the levels of total bacterial count (TBC), psychrotrophic bacteria count (PBC) and Pseudomonas spp. count (PSC), during cold preservation. Raw buffalo milk samples supplemented with esterified legume proteins have reached a TBC log of 5.1-5.3 cfu ml⁻¹ surpassing the spoilage level after a relatively longer period (6 days) than in the case of non-supplemented raw milk (2 days). At the end of storage period, acidity level reached comparatively higher maximum values in the untreated raw milk (0.74 ± 0.018) compared to lower values in case of milk supplemented with esterified legume proteins (0.52 ± 0.011 to 0.55 ± 0.012). At the same time corresponding pH values of the untreated raw milk attained a lower minimum values in case of raw milk supplemented with esterified legume proteins than in non-treated raw milk. Some casein degradation started in non-treated raw milk after 2 days of preservation at 4 °C and complete casein degradation was observed after 4 days. Casein remained nearly intact in raw milk supplemented with esterified proteins for 10 days. Supplementation with esterified legume proteins has substantially delayed the coagulation response to the 8 and 10 days of preservation at 4 °C, instead of 4 days in case of the control.     

A study of the growth of Lactobacillus acidophilus in bovine, ovine and caprine milk

The fermentation of reconstituted bovine, ovine and caprine milks with Lactobacillus acidophilus was investigated. Better growth of Lb. acidophilus was observed in ovine milk, but higher acidities developed in caprine milk. The high acidity produced after 12 h of fermentation (pH 3.9) created a hostile environment for the survival of the microorganism in caprine milk.     

Cheesemaking with vegetable coagulants—the use of Cynara L. for the production of ovine milk cheeses

This paper reviews the use of plant extracts as vegetable coagulants for cheesemaking. It covers the plants used as sources of coagulants, with a historical overview and particular emphasis on Cynara species. The genus Cynara  L., its composition, milk clotting and proteolytic enzymes (cardosins) and their specificity towards peptide linkages are also described. Cheeses produced in the Iberian Peninsula using Cynara  L. as coagulant are documented. Cynara  L. is still the most used vegetable coagulant in cheesemaking, and also the most investigated. However, much work remains to be done to understand its action during cheese maturation and further characterization.     

Stability of cyclopiazonic acid during storage and processing of milk

The effect of refrigerated storage (4°C) of raw or processed milk on the stability of cyclopiazonic acid (CPA) in milk was investigated. CPA decreased by 1.4% following 4 days of simulating collecting, storing and transporting of contaminated (1 μg CPA ml⁻¹) raw milk. Storage at 4°C for 21 days, simulating retail milk, moderately reduced the CPA level by 5.8%. A similar trend of CPA decrease was observed in frozen and freeze dried milk stored at −18°C. However, in both products, less than 12% of CPA decreased in spite of a storage period of 140 days. The effect of processing milk on component separation of CPA was also studied. Simulating unsweetened condensed milk production by preheating 4 l contaminated milk to 100°C and concentrating under steam injection to 1.5 l led to a decrease of CPA by 39.7%. In contrast, very little CPA (0.7%) was lost from the production of evaporated milk using low temperature (60°C) heating under vacuum to remove water. CPA was stable in both concentrated and evaporated milks throughout an 8 weeks storage period at 4°C. There was no decrease of CPA during the manufacturing of milk powder by spray drying. Persistence of CPA during the above milk storage and processing methods confirmed the potential of CPA to reach consumers of dairy products when the mycotoxin was carried over into processed milks.     

Identity of the major triacylglycerols in ovine milk fat

Ovine milk fat obtained from milk collected from five different flocks was studied to determine its triacylglycerol (TAG) composition using a combination of gas chromatography/mass spectrometry. One hundred and thirty-four molecular species of TAG were identified, but not all could be quantified because some peaks contained more than one species of TAG. Fifty-one per cent of the identified species were trisaturated TAGs, 31% as monounsaturated TAGs and 18% as polyunsaturated TAGs. In terms of chain length, 58 of the TAGs identified (43% of the total) contained short-chain (C4 and C6) fatty acids (FAs), 94 (70%) contained medium-chain FAs (C8–C14) and 112 (84%) were composed of long-chain FAs (C16–C18). One hundred and twenty nine chromatographic peaks were detected. The sum of the 35 peaks, each representing>1 mol% of the TAGs, was 75% of total TAGs. Five peaks, each with>3.5 mol% included trisaturated and monounsaturated TAGs; quantitatively, the largest of these peaks (4.5 mol% of the total TAGs) contained two esterified monounsaturated TAGs with C4: 4,16,18:1 or 4,18,16:1, with the former being present at the highest levels. Comparison of the experimental values of TAG composition in ovine milk with the theoretical values derived from the experimental FA content showed that the distribution of the FAs in the TAGs was not random. The TAGs containing a short-chain FA were synthesized preferentially to those TAGs containing three medium- or three long-chain FAs. Our results for ewes’ milk were very similar to those for cows’ and goats’ milk despite the quantitative differences in the TAG profiles of the different species.     

Development of flavour defects in pasteurized double cream during storage at 6°C and at 10°C

A total viable count in excess of 1× 10⁷ cfu/ml is required before organoleptic defects can be detected in pasteurized double cream, although defects were shown to be the results of non-bacterial sources in creams from one creamery in the survey. Proteolysis was associated mainly with the presence of Bacillus spp. and resulted in the detection of a bitter flavour in the creams.     

Bioactive amines changes in raw and sterilised milk inoculated with Pseudomonas fluorescens stored at different temperatures

The presence of bioactive amines in raw and sterilised milk inoculated with Pseudomonas fluorescens during storage at 4°C, 7°C and 10°C for 6 days was investigated. Spermine, spermidine, putrescine, serotonin and phenylethylamine were present in the samples immediately after milking. Histamine, cadaverine and tyramine were formed in the raw milk on the 4th day of storage at 10°C, increasing significantly afterwards. Cadaverine was formed during sterilisation. There was no significant change in amines, acidity, thermostability and alizarol tests throughout storage of the sterilised milk; however, a putrid smell was detected at every temperature on the 6th day. Therefore, raw or sterilised milk storage at 4–7°C should not exceed 4 days. Furthermore, raw milk should not be stored at 10°C.     

不同体细胞数原料乳对UHT贮存期间蛋白和脂肪水解的影响

不同体细胞数(21.4×104mL-1,75.8×104mL-1,118.1×104mL-1和216.2×104mL-1)原料乳生产的4组UHT乳在37℃贮存84d,对其贮存期间的蛋白水解及脂肪水解进行研究。结果表明,4组UHT乳贮存期间的蛋白水解速率无显著性差异(P>0.05),原料乳体细胞数并未对蛋白水解造成影响;4组UHT乳贮存期间的脂肪水解速率具有显著性差异(P<0.005),原料乳体细胞数与脂肪水解速率间存在极明显的正相关(R=0.9886,P<0.05)。     

Nucleotides and nucleosides in ovine and caprine milk during lactation

The aim of this study was to determine the nucleoside and nucleotide content in ovine and caprine milks at the colostral, transitional, and mature stages of lactation. Samples from 18 dairy sheep and 18 dairy goats were collected at 1, 2, 3, 4, 5, and 15 d postpartum. Separation and quantitation of the 5′-nucleotides (NT) and the nucleosides (NS) was performed by reverse phase HPLC. For each compound measured, considerable interindividual variation was recorded in both species of milk. The total NS content ranged from 57 to 132 μmol/L and from 54 to 119 μmol/L in ovine and caprine milk, respectively. The major NS identified in both species of milk was uridine, representing more than 60% of the total NS pool. The mean levels of inosine and guanosine were comparable between ewe and goat milk. Instead, the mean level of cytidine across the sampling period was much higher in ewe milk (11.9 μmol/L compared with 4.5 μmol/L in goat milk) and exhibited a peak value on the fourth day of lactation. The adenosine content was at least 3-fold higher in caprine milk compared with its ovine counterpart. The total NS and orotic acid contents did not differ significantly between the 2 species. However, in the case of total NT content, interspecies differences were significant, with NT levels ranging from 294 to 441 μmol/L in ovine milk and from 166 to 366 μmol/L in caprine milk. The NT content in colostrum (1-3 d) of both species was higher than in mature milk (15 d), and uridine monophosphate was the dominant NT in all samples.