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.     

新鲜软质干酪加工工艺的研究

以鲜牛乳为原料,研究了新鲜软质干酪的制作工艺,采用L9(34)正交试验的方法,研究了不同发酵剂菌种添加比例、发酵温度、切割pH值对成品干酪滋味口感、色泽和涂抹性的影响,最终确定了该产品生产的最佳配方和工艺条件:菌种比为1:1(质量比),发酵剂添加量为3%(质量分数),发酵温度为37℃,切割pH值为4.6。     

天然奶酪对再制奶酪理化性质的影响

研究了天然干酪的添加量及其成熟度对再制奶酪理化性质及功能特性的影响。结果表明:再制奶酪的完整酪蛋白质量分数、储能模量、损耗模量和硬度均随着天然奶酪的添加量及其成熟度的增加而呈现下降趋势,而再制干酪的风味及组织状态则不然;成熟度为1月和4月的天然Mozzarella干酪配比为2︰1时,产品的功能特性及口感最佳。     

Effect of various high-pressure treatments on the properties of reduced-fat Cheddar cheese

A major problem with reduced-fat cheese is the difficulty in attaining the characteristic flavor and texture of typical full-fat versions. Some previous studies have suggested that high hydrostatic pressure (HHP) can accelerate the ripening of full-fat cheeses. Our objective was to investigate the effect of HHP on reduced-fat (~7.3% fat) Cheddar cheese, with the goal of improving its flavor and texture. We used a central composite rotatable design with response surface methodology to study the effect of pressure and holding time on the rheological, physical, chemical, and microbial characteristics of reduced-fat Cheddar cheese. A 2-level factorial experimental design was chosen to study the effects of the independent variables (pressure and holding time). Pressures were varied from around 50 to 400 MPa and holding times ranged from 2.5 to 19.5 min. High pressure was applied 1 wk after cheese manufacture, and analyses were performed at 2 wk, and 1, 3, and 6 mo. The insoluble calcium content as a percentage of total Ca in cheeses were not affected by pressure treatment. Pressure applications ≥225 MPa resulted in softer cheese texture during ripening. Pressures ≥225 MPa increased melt, and resulted in higher maximum loss tangent values at 2 wk. Pressure treatment had a greater effect on cheese microbial and textural properties than holding time. High-pressure-treated cheeses also had higher pH values than the control. We did not observe any significant difference in rates of proteolysis between treatments. In conclusion, holding times of around 5 min and pressures of ≥225 MPa could potentially be used to improve the excessively firm texture of reduced-fat cheese.     

水分含量对新鲜干酪贮藏特性的影响

对水分含量不同的4组干酪进行贮藏期水分含量、水分活度、pH、酸价、TBA值测定和感官评定。结果表明:干酪水分含量与水分活度随贮藏期呈递减趋势,并且呈正相关关系;酸价随着贮藏期的延长先增加后减少;pH则相反,呈先下降后上升的趋势;TBA值呈逐渐上升趋势。表明水分含量低的干酪,其耐贮藏性较好。感官特征测定在贮藏的第18d开始,干酪逐渐开始出现腐败特征,水分含量较低的干酪感官评分高。     

Effect of processing steps on the physico-chemical properties of dried-seasoned squid

The effects of processing steps on the physico-chemical properties of dried-seasoned squid were studied using two kinds of squids. Browning was observed as indicated by an increase in yellowness (b^∗ value) during the semi-drying and roasting step. The temperature and time of heating and type of roasting, as well as the material itself were the key factors influencing the browning. A high level of trimethylamine oxide (TMAO), and low contents of trimethylamine (TMA) and dimethylamine (DMA) were detected in the raw material. TMAO gradually decreased during the processing, while TMA, DMA and formaldehyde (FA) increased significantly especially in boiled meat. The temperature of boiling was the most crucial factor impacting the production of FA. FA could be greatly decreased during the cooling process by washing with water or changing the roasting techniques. Therefore, to improve the quality of dried-seasoned squid, more attention should be paid to the temperature and roasting techniques during the processing.     

The effect of ultra high-pressure homogenization (UHPH) on rennet coagulation properties of unheated and heated fresh skimmed milk

The effect of ultra-high pressure homogenization at a pressure of 179 MPa on the renneting of milk has been studied. The homogenization has a small effect on the diameters of casein micelles, because of the loss of some of their surface κ-casein. This modification of the structure leads to a slightly decreased rennet coagulation time. Interactions between the casein micelles in homogenized and unhomogenized milk samples started at a degree of proteolysis of the κ-casein of about 65–70%, although aggregation of the micelles did not start until over 90% proteolysis. Homogenization improved the coagulation properties of heated milk only slightly; however, it was shown that the removal of stabilizing repulsions between the casein micelles in the heated milk seemed to proceed in the same way as in unheated milk. The removal of the κ-casein has the same effect in heated and unheated milk samples, and the casein micelles are destabilized; it is only in the final aggregation step that the two milks differ.     

Textural and microstructural properties of urfa cheese (a white-brined Turkish cheese)

The texture and microstructure of white-brined cheeses similar to urfa (a traditional Turkish cheese) were studied. One batch of cheeses was made in the traditional manner and one batch was made from ultrafiltered (UF) milk. Samples from each batch were either ripened in brine after production or scalded in whey for 3 min at 90°C prior to ripening. The results showed only marginal differences in the ripening profiles of both batches of unscalded cheeses, but scalding slowed down the extent of proteolysis in both batches. The scalded cheeses had a firmer texture than the unscalded ones, and the unscalded UF cheese had a more 'springy' body than the unscalded traditional cheese. Overall, scalding resulted in a more homogeneous structure, but the unscalded UF cheese had a close texture that resembled the scalded samples. It was concluded that, with respect to texture and structure, cheeses made with UF milk do not need to be scalded after production.     

Influence of transglutaminase treatment on some physico-chemical properties of milk

Transglutaminase (TGase) is an enzyme that cross-links many proteins, including milk proteins. In this study, the effects of TGase on some physico-chemical properties of milk were studied. TGase-treated milk was not coagulable by rennet, which was due to failure of the primary (enzymic) stage of rennet action rather than the non-enzymic secondary phase. Dissociation of TGase-treated casein micelles by urea or sodium citrate or removal of colloidal calcium phosphate by acidification and dialysis was reduced, presumably due to the formation of cross-links between the caseins. Casein micelles in TGase-treated milks were also resistant to high pressure treatment and to hydrolysis by plasmin. Results of the present study show that milk proteins are fundamentally modified by the action of TGase, which may have applications in the manufacture of functional proteins for use as novel food ingredients.     

Influence of processing parameters on the texture and microstructure of imitation cheese

In this study the impact of cooker design and/or blade/auger speed on the functional properties of imitation cheese was investigated. Cheeses with similar compositions (48% moisture) were manufactured using water, rennet casein, rapeseed and hydrogenated palm oil and emulsifying salts in a twin-screw (Blentech) or a single-blade cooker (Stephan). The cookers were operated at auger speeds of 750, 1,125 or 1,500 (Stephan) or 100 or 200 rpm (Blentech). Increasing the blade speed of the Stephan increased (P < 0.001) the hardness and decreased the meltability of imitation cheese from 112 to 66 mm respectively. Hardness and meltability values of cheeses made in the Blentech cooker were only slightly affected by auger speed. The cheese made in the Stephan at 1,500 rpm had the highest G′ and G′′ values at 25 °C of all the cheeses. This study shows that imitation cheese with acceptable functional properties can be successfully manufactured in a single-blade cooker operated at moderate speeds.     

工艺参数对再制干酪的质构和流变性质的影响

利用质构仪和流变仪对影响再制干酪品质的多个因素进行了研究。结果表明，水分影响再制干酪的质构和流变性质：乳化盐对再制干酪产品的质构没有显著的影响；不同的温度和不同的搅拌时间对样品的质构有着相似的变化；在所有加工条件下．再制干酪的G′始终大于G″，G′和G″没有交叉点，而且复合黏度η^＊随着频率的增加而急剧降低，体系表现出了弱凝胶的特性。     

Effect of high pressure on fresh cheese shelf-life

The effect of high pressure (HP; 300 and 400 MPa for 5 min at 6 °C) on physico-chemical, microbial, color, texture and sensorial characteristics of starter-free fresh cheeses stored at 4 and 8 °C was studied. Physico-chemical parameters considered were total solids, fat, total protein, pH, whey loss and water activity. The microbiological quality was studied, on cheeses stored at 4 and 8 °C, by enumerating aerobic mesophilic bacteria, lactococci, psychrotrophic bacteria, Enterobacteriaceae, Escherichia coli, molds and yeasts. Cheeses treated at 300 and 400 MPa, stored at 4 °C, presented a shelf-life of 14 and 21 days, respectively, compared to untreated control cheese, which presented a shelf life of 7 days. On the other hand, HP treatments modified the texture (more firm) and color (more yellow) compared to control cheeses. These changes were detected by instrumental and sensory analysis.     

鲜茧缫丝蚕蛹油与新鲜蚕蛹油理化性质及组分分析

鲜茧缫丝是不经过高温烘茧、煮茧以及强碱浸泡的缫丝工艺。基于高效利用鲜茧缫丝蚕蛹的目的,本文通过提取鲜茧缫丝蚕蛹油和新鲜蚕蛹油,并对2种油脂脂肪酸的理化性质和组分进行比较分析。结果表明:2种蚕蛹油在皂化值、酸价值、碘值、过氧化值4个理化指标方面存在差异,但差异性不大;且2种蚕蛹油脂肪酸的组成与相对含量存在的差异也不明显。     

Ultrasonic assessment of fresh cheese composition

Fresh cheese composition was assessed by measuring ultrasonic velocity in cheese and cheese blends at different temperatures. Twenty types of commercial, fresh cheeses with fat contents ranging from 0.2% to 17.6% w.b. were analyzed. Ultrasonic velocity was not only heavily dependent on the composition of the cheese but also on its structure. Based on the different effect temperature has on velocity in water and fat, a semi-empirical model was used to estimate the cheese composition from velocity measurements at six temperatures ranging from 3 to 29 °C. The model provided good results for the assessment of the fat (R² = 0.984/0.996; RMSE = 4.6/1.1 for whole and blended cheese, respectively) and water (R² = 0.964/0.995; RMSE = 6.5/0.7 for whole and blended cheese, respectively) content. The ultrasonic measurements could be carried out during the cooling process that takes place after curdling and used as a quality control tool to detect process anomalies in-line.     

Effect of processing on the physico-chemical properties of African yambean,Sphenostylis stenocarpa (Hochst ex A. Rich) Harms

Soaked and heat-trated yambean seeds were studied for some of their chemical and physical characteristics. An increase of between 2.9 and 29.4% in the ash contents reflected mineral pick-up by seeds pre-soaked in salt solutions. Subsequently, remarkable losses of Ca. K. and Na resulted when seeds pre-soaked in salt solutions were cooked. Roasting also caused a substantial loss of Ca. A phytic acid loss by 4.5 to 36.7% was obtained by soaking and heat treatment of yambeans. Trypsin inhibitor activity (TIA), although decreased substantially with cooking, slightly increased during the pre-soaking step. Alkali and alkali-brine soaked seed flours, with a water-oil-absorption index of about 2.0, exhibited the best hydrophilic-lipophilic balance.     

用芝士粉生产芝士酱工艺条件的研究

以芝士粉为原料,通过对不同增稠剂、乳化剂对产品工艺、品质的影响,确定以芝士粉为原料,生产理想的芝士酱配方为水53.7%,黄油20%,28020芝士粉13%,乳清粉10%,六偏磷酸钠1.0%,焦磷酸钠0.5%,黄原胶0.25%,明胶2.0%(w/w);工艺条件为: pH5.6～6.2,乳化温度70℃,乳化时间6min.     

不同加工方法对鲜乳中Vc含量的影响

研究了不同的加工方法对乳制品中Vc含量的影响。采用分光光度法进行测定,并比较了6种不同乳样中Vc的含量,从而得出最佳的鲜乳加工方法。结果表明：以超高瞬时灭菌法（UHT）对鲜乳中Vc的破坏最小,损失率仅为9.0%。