Comparative Electrochemical Determination of Total Antioxidant Activity in Infant Formula with Breast Milk

The aim of this study is to investigate the significance of breast milk and infant formula in the prevention of oxidative stress, by electrochemical determination of the total antioxidant potential, demonstrating the relationship between the antioxidant capacity of milk and postnatal age. Human breast milk, commercial UHT milk, and infant formulas supplemented with prebiotics were used. Samples were diluted in phosphate buffer solution, and the total antioxidant activity was potentiometrically measured by the iodine/iodide redox couple with the Pt Fisher electrode as a working electrode and saturated calomel as a reference electrode. Cyclic voltammograms and differential pulse voltammograms were recorded with the glassy carbon electrode as the working electrode, an accessory platinum electrode, and an Ag/AgCl reference electrode. The potentiometric measurement indicates that human breast milk has the highest redox potential, while the commercial UHT milk has very low potential. Infant formulas also have high potential. The main advantage of electrochemical methods used to assess the total antioxidant activity of milk was that they directly monitored the electron-donating ability of the compounds and could be used for the quantitative analysis of the total antioxidants of different types of milk.     

不同工艺参数对Mozzarella干酪质构和功能特性的影响

采用三因素二次通用旋转组合设计,研究热缩温度、堆酿pH、拉伸温度等关键工艺参数对全脂Mozzarella干酪的质构特性(硬度、凝聚性、弹性)和功能特性(融化性和油脂析出性)的影响规律,结果表明提高热缩温度可增加干酪硬度及干酪的油脂析出性;提高拉伸温度也可增加干酪的油脂析出性;堆酿pH对干酪的弹性有较大影响,随着堆酿pH的降低,干酪的弹性增大,并与热烫拉伸温度之间有交互作用,即低的堆酿pH和高的拉伸温度时干酪的弹性大。     

Causes and control of early gas production in cheddar cheese

Early gas production in cheddar cheese is a sporadic and recurrent problem. In this article the major causal agents of unwanted gas production are discussed and potential gas producing organisms in cheddar cheese are identified. Results of investigations of gas production in commercial plants and control measures are presented. It is concluded that early gas production in cheddar cheese results from a number of interacting factors, including lactose and citrate levels in the curd, the temperature of curd/cheese during pressing and curing, the salt in moisture level and the levels of gas producing, non-starter lactic acid bacteria in the cheese.     

The effect of natural cheddar cheese ripening on the functional and textural properties of the processed cheese manufactured therefrom

ABSTRACT:  Cheddar cheese ripened at 8 °C was sampled at 7, 14, 28, 56, 112, and 168 d and subsequently used for the manufacture of processed cheese. The cheddar cheese samples were analyzed throughout ripening for proteolysis while the textural and rheological properties of the processed cheeses (PCs) were studied. The rate of proteolysis was the greatest in the first 28 d of cheddar cheese ripening but began to slow down as ripening progressed from 28 to 168 d. A similar trend was observed in changes to the texture of the PC samples, with the greatest decrease in hardness and increase in flowability being in the first 28 d of ripening. Confocal scanning laser microscopy showed that the degree of emulsification in the PC samples increased as the maturity of the cheddar cheese ingredient increased from 7 to 168 d. This increased emulsification resulted in a reduction in the rate of softening in the PC in samples manufactured from cheddar cheese bases at later ripening times. Multivariate data analysis was performed to summarize the relationships between proteolysis in the cheddar cheese bases and textural properties of the PC made therefrom. The proportion of α _{s 1}-casein (CN) in the cheddar cheese base was strongly correlated with hardness, adhesiveness, fracturability, springiness, and storage modulus values for the corresponding PC. Degradation of α _{s 1}-CN was the proteolytic event with the strongest correlation to the softening of PC samples, particularly those manufactured from cheddar cheese in the first 28 d of ripening.     

Effect of calcium and phosphorus, residual lactose, and salt-to-moisture ratio on the melting characteristics and hardness of cheddar cheese during ripening

ABSTRACT:  Meltability, melt profile parameters, and hardness of cheddar cheese prepared with varying levels of calcium (Ca) and phosphorus (P) content, residual lactose content, and salt-to-moisture ratio were studied at 0,1, 2, 4, 6, and 8 mo of ripening. Meltability, melt profile parameters, and hardness of cheddar cheeses measured at 0, 1, 2, 4, 6, and 8 mo of ripening showed significant interaction between the levels of Ca and P, residual lactose, salt-to-moisture ratio, and ripening time for most of the properties studied. cheddar cheese prepared with high Ca and P (0.67% Ca and 0.53% P) resulted in up to 6.2%, 4.5%, 9.6%, 5.0%, and 22.8% increase in softening time, softening temperature, melting time, melting temperature, and hardness, respectively, and 23.5%, 9.6%, and 3.2% decrease in meltability, flow rate, and extent of flow, respectively, compared to the cheddar cheese prepared with low Ca and P (0.53% Ca and 0.39% P). cheddar cheese prepared with high lactose (1.4%) content resulted in up to 7.7%, 7.0%, 4.9%, 4.2%, and 24.6% increase in softening time, softening temperature, melting time, melting temperature, and hardness, respectively, and 14.7%, 12.7%, and 2.8% decrease in meltability, flow rate, and extent of flow respectively compared to the cheddar cheese prepared with low lactose (0.78%) content. cheddar cheese prepared with high salt-to-moisture ratio (6.4%) resulted in up to 21.8%, 11.3%, 12.9%, 4.1%, and 29.4% increase in softening time, softening temperature, melting time, melting temperature, and hardness, respectively, and 13.2%, 28.6%, and 2.6% decrease in meltability, flow rate, and extent of flow, respectively, compared to the cheddar cheese prepared with low salt-to-moisture ratio (4.8%) during ripening.     

The influence of milk pasteurization temperature and pH at curd milling on the composition, texture and maturation of reduced fat cheddar cheese

Reduced fat milks were pasteurized, for 15 s, at temperatures ranging from 72 to 88°C to give levels of whey protein denaturation varying from ˜ 3 to 35%. The milks were converted into reduced fat cheddar cheese (16–18% fat) in 500 litre cheese vats; the resultant cheese curds were milled at pH values of 5.75 and 5.35. Raising the milk pasteurization temperature resulted in impaired rennet coagulation properties, longer set-to-cut times during cheese manufacture, higher cheese moisture and moisture in the non-fat cheese substance, lower levels of protein and calcium and lower cheese firmness. Increasing the pH at curd milling from 5.35 to 5.75 affected cheese composition and firmness, during ripening, in a manner similar to that of increasing milk pasteurization temperature. Despite their effects on cheese composition and rheology, pasteurization temperature and pH at curd milling had little influence on proteolysis or on the grading scores awarded by commercial graders during ripening over 303 days .     

成熟温度和时间对Cheddar干酪成熟特性的影响研究

通过对不同成熟参数下Cheddar干酪蛋白分解、质构、pH及感官评价的分析,探讨了成熟参数对Cheddar干酪的影响,并得出研究条件下的最优成熟温度和时间,分析了Cheddar干酪在成熟过程中的游离氨基酸变化情况。     

Protein Quality of Cheddar Cheese Compared with Casein and Fabricated Cheese in the Rat

The protein quality of freeze-dried cheddar cheese, spray-dried cheddar cheese, freeze-dried fabricated cheddar cheese (with casein as the main protein source), and sodium caseinate was evaluated in rats using the protein efficiency ratio (PER) assay (AOAC procedures) in two feeding experiments with casein as the control. Biological evaluation of the products showed that PER values for freeze-dried cheddar cheese were significantly higher than casein (3.7 vs 2.5). Freeze-dried cheddar also had a PER value significantly higher than spray-dried cheddar cheese (3.7 vs 3.0). Freeze-dried fabricated cheddar cheese and sodium caseinate had PER values not significantly different from the casein control.     

Development of a Rat Model to Test the Nutritional Equivalency of Traditional vs Fabricated Foods: Cheddar Cheese vs Fabricated Cheddar Cheese

Based on the Food & Drug Administration's proposed 1978 standards for “nutritional equivalency,” we have developed a biological assay designed to test the “nutritional equivalency” of traditional vs fabricated foods using cheddar cheese and fabricated cheddar cheese as examples. Diets were formulated that lacked the FDA proposed vitamin and mineral requirements (riboflavin, vitamins B-12 and A, calcium, phosphorus, zinc) for cheese substitutes. By adding traditional or fabricated cheddar cheese to such diets, we were able to compare the overall presence and bioavailability of the vitamins/minerals required for nutritional equivalency. Throughout the 28 day test, the fabricated cheddar cheese did not support the growth of male Sprague-Dawley rats as well as cheddar cheese did.     

切达干酪促熟附属发酵剂的筛选

切达干酪成熟时间较长,成熟期间费用较高,导致生产成本增加。因此干酪的促熟受到人们的普遍关注。试验从中国传统发酵食品中分离出12株具有较高肽酶活力的菌株,经进一步筛选,得到了两株具有较好促进干酪成熟能力的菌株,有望作为附属发酵剂应用于切达干酪生产。     

Quality of Processed Cheddar Cheese as a Function of Emulsifying Salt Replaced by κ-Carrageenan

Hydrocolloids act as stabilizer and thickening agents, thus able to replace emulsifying salts. The present study was planned to use к-carrageenan in the production of processed cheddar cheese and to explore its effect on physico-chemical and textural properties of processed cheddar cheeses. Different concentration of ?-carrageenan were used with gradual decrease in salt contents along with natural cheese, fat, and water to prepare processed cheddar cheese. The prepared samples were analyzed for physico-chemical and sensory attributes at storage interval of 45 days during and after 90 days. With the increase in hydrocolloid concentration, stiffer product was obtained and meltability of the samples decreased than control. Processed cheddar cheese samples having 0.15% к-carrageenan with 2% emulsifying salt (1.34% sodium citrate and 0.66% disodium phosphates) were found more acceptable in terms of physico-chemical and sensory attributes, but all sensory attributes got fewer score with the passage of storage time.     

Cheddar干酪附属发酵剂筛选及其应用

为了筛选能够促进Cheddar干酪成熟,从泡菜、腐乳及不同产地的Cheddar中筛选具有高肽酶活力和自溶度的乳杆菌作为Ched-dar干酪附属发酵剂,并应用于Cheddar干酪的制作中.结果表明,从美国Cheddar干酪中筛选出1株Lactobacillus plantarum OD具有较高的肽酶活力和自溶度,运用于Cheddar千酪的制作中能显著提高其游离氨基酸浓度,改善其风味,有利于加快干酪的成熟.     

Textural Changes of Natural Cheddar Cheese During the Maturation Process

ABSTRACT: Texture parameters of commercial natural cheddar cheese were tracked over the maturation period (11-mo) but not to evaluate optimal or desirable characteristics. Large strain analysis was performed using the TA-XT2 Texture Analyzer. Monitoring of chemical composition and degree of proteolysis and the solid proportions of milk fat were undertaken with differential scanning calorimeter. Fracture properties, force, and degree of compression confirmed a reduction in cheese firmness and an increase in cheese crumbliness during maturation. Increases in the concentration of small peptides, indicating enhanced proteolytic activity, and an increase in the proportion of solid fat at 21 °C late in maturation were considered primarily responsible for the changes recorded in cheese texture.     

毛细管电泳-电化学检测法测定鸡蛋中残留四环素类抗生素

本研究运用毛细管电泳-电化学检测法(CE-ED)对鸡蛋中残留的四环素(TC)、土霉素(OTC)进行快速测定分析。考察了缓冲液浓度和pH值、TW-20、盐浓度、分离电压、进样时间、检测电位等因素对分离检测的影响。结果表明,TW-20体积分数为2.5%时,在检测电位为1.2V,20mmol/L缓冲溶液(pH2.6),25kV分离电压,进样8s的条件下,TC和OTC有很好的分离效果。TC和OTC的线性范围分别为:2.0×10-6～5.0×10-4g/ml和8.0×10-6～3.0×10-4g/ml,检测限分别为1.9×10-8g/ml和4.1×10-8g/ml。     

Continuous monitoring of yoghurt fermentation using a noble metal electrode array

An electrochemical probe containing gold, platinum and rhodium working electrodes was used to monitor yoghurt production in a pilot facility. Three commercial starting cultures at 40, 42 and 44 °C transformed milk having 1.5% fat content to mild yoghurt products. The electrochemical changes in the broth during fermentation were recorded as current responses from pulse voltammetry over the electrodes. Principal component analysis of the responses generated two-dimensional score plots describing the qualitative fermentation progressions. Two distinct fermentation pathways were observed leading to similar final products. The pH was recorded during the fermentations and the data was used as reference values for creating a partial least squares model for prediction of pH as an example of a quantitative application for the sensor. The relative mean squared error for validation of the model using four probes interchangeably was about 2%. The probe was constructed of materials approved for use in the food industry and did not require a standard glass reference electrode.     

Fermentation of specially formulated milk with single strains of bifidobacteria

A number of strains of bifidobacteria have been used to ferment milk to a yoghurt-like product. The milk used for fermentation was fortified with whey protein and threonine. It was prepared by mixing skimmed milk and cheddar cheese whey which had been concentrated using ultrafiltration membranes which allowed lactose to permeate. A 2 percent inoculum was used, and fermentation was carried out at 37° C overnight. The resulting products resembled voghurt, having good consistency. 'walnutty' aroma (acetaldehyde). and pleasant acidity.     

Detection of cheese packaging containment failures using reversible optical oxygen sensors

This study investigated the capacity of optical oxygen sensors to nondestructively detect containment packaging failures in commercial vacuum packed cheddar cheese. Unacceptable oxygen levels in packs lead to product deterioration and can significantly reduce shelf life. Vacuum packed cheddar cheese was monitored for oxygen levels over time at 4 °C with optical sensors prefitted to packaging laminates polyethyleneterephthalate/polypropylene. Oxygen levels present in packs immediately after packaging were 3% on average. Further ingress of oxygen into all packs occurred over storage time and levels ranged from 3.6% to 8.2% after 6 days. Information obtained using oxygen sensors led to further assessments and identification of the causes of packaging containment failure.     

Comparison of Four Procedures of Cheese Meltability Evaluation

Two traditional cheese meltability tests, the Schreiber and Arnott, as well as two microwave modifications thereof were compared on a variety of mild and sharp cheddar, process American, and mozzarella cheeses and various process cheese products. There was a marked lack of correlation between the Schreiber and Arnott results indicating that at least two material properties control meltability. The effects of variations in heating time and oven temperature in the nonmicrowave tests and heating time in the microwave tests were determined. Differential scanning calorimetry did not reveal differences useful in predicting melting behavior.     

Sensory properties of low fat cheddar cheese:effect of salt content and adjunct culture

The influence of salt concentration and of direct-to-vat culture adjuncts (DVCA) on the sensory properties of low fat hard cheese of the cheddar type has been investigated. Salt content has a major influence, and, at a level of 1·8%, low fat cheese with high levels of cheddar flavour and low bitter scores was produced. In addition, further enhancement of flavour was achieved by use of DVCA. Using the methodology described in this report, low fat cheese was manufactured which corresponded in flavour level and balance to that of commercial mature full fat cheese. Nevertheless, textural differences between low fat and full fat product remain to be resolved.