EVALUATION OF pH CHANGE KINETICS DURING DIFFERENT STAGES OF KASHAR CHEESE PRODUCTION FROM BOVINE, OVINE AND CAPRINE MILK

The objective of this study was to determine the pH change kinetics during Kashar cheese production from bovine, ovine and caprine milk. Kinetics of pH change were determined during milk ripening, cooking/holding and pressing/fermentation phases of Kashar cheese. The pH decreased logarithmically, nonlinearly, with time in the milk ripening period and was reduced linearly with time in the cooking/holding and pressing/fermentation stages. The time of pH decrease in cow's, ewe's and goat's milk was significantly different, except cooking/holding time, for three stages. There was no difference between bovine and caprine milk in cooking/holding time; however, ovine milk was significantly different from the other two kinds of milk. The shortest and the longest overall times were determined for caprine and ovine milk cheeses, respectively. The rate of change in milk pH of the three species was significantly different for three stages. The rate followed the pattern caprine  >  bovine  >  ovine milk.

PRACTICAL APPLICATIONS

Optimum acid development is essential to creating the desired cheese mass. For each major cheese type, lactic acid must develop in the appropriate time, usually not too rapidly or too slowly, and in a specific concentration. The progress of acidification is monitored by pH change in the industrial Kashar cheese production. The final pH of cheese is determined not only by the amount of lactic acid but also by the buffering capacity (BC) of the milk and curd. However, the BC is different between milk species. This study evaluates and compares the pH change kinetics during various stages of Kashar cheese making using cow's, ewe's and goat's milk. This work may help to compare milk and cheese curds made from bovine, ovine and caprine milk.     

HIGH-PRESSURE DESTRUCTION KINETICS OF SPOILAGE AND PATHOGENIC BACTERIA IN RAW MILK CHEESE

Raw milk cheese samples were individually inoculated with Escherichia coli K‐12, Escherichia coli O157:H7 and Listeria monocytogenes, and subjected to high‐pressure (HP) treatments (200–400 MPa) in both pressure hold and pressure pulse modes. Pressure inactivation of E. coli K‐12 at 350 MPa (5 min) at different temperatures demonstrated a strong temperature effect when temperature was 40C and above. Pressure destruction kinetics and pressure sensitivity were evaluated at 25C (where the temperature effect was minimal). HP treatment generally demonstrated a step‐change pressure pulse effect followed by a holding time destruction that was well described by a first‐order model (R² > 0.90) with higher pressures resulting in a faster rate of microbial reduction (smaller D values). The associated D values at an intermediate pressure of 300 MPa were 4.4, 14.5 and 3.6 min for E. coli K‐12, E. coli O157:H7 and L. monocytogenes, respectively, with E. coli O157:H7 thus demonstrating a higher‐pressure resistance than the other two. The corresponding pressure z_p values were 156, 128 and 82 MPa, and ΔV^≠(Arrhenius volume change of activation) values were ?3.6, ?4.4 and ?7.0 (×10^?5 m³/mole), respectively. Pulse mode treatments showed similar pressure resistance trends to pressure hold mode, but were not effective for E. coli O157:H7.     

SENSORY CHARACTERISTICS OF EWE MILK CHEESE MADE WITH THREE TYPES OF COAGULANT: CALF RENNET, POWDERED VEGETABLE COAGULANT AND CRUDE AQUEOUS EXTRACT FROM CYNARA CARDUNCULUS

This article reports on a study of the sensorial characteristics of ewe milk cheese (Los Pedroches) made with animal rennet and two types of coagulant obtained from the cardoon Cynara cardunculus. The cheeses made with rennet displayed a less odor intensity: pungent odor and acid odor; a less acid taste; and a slightly lighter color. They were harder and firmer, but less creamy than those made with the vegetable coagulant (powdered vegetable coagulant [PVC] and crude aqueous extract [CAE] from C. cardunculus). However, the cheeses made with PVC showed organoleptic characteristics very similar to the cheeses made with CAE from C. cardunculus. After 90 days' ripening, the cheeses made with vegetable coagulant displayed a slightly more bitter taste than those made with rennet. In general terms, increased ripening time prompted the increased scores for most of the sensory attributes studied.     

OCCURRENCE OF AFLATOXIN M1 IN RAW MILK DURING THE SUMMER AND WINTER SEASONS IN HAMEDAN, IRAN

A survey on the occurrence of aflatoxin M₁ (AFM₁) was carried out in summer and winter in raw milk samples from 93 traditional and industrial dairy farms of the Hamedan district in order to address representative data on AFM₁ in milk collected from these regions. Of the 186 milk samples, AFM₁ was detected in 119 samples (63.97%). The mean concentration of AFM₁ in contaminated samples was 43.4 ng/L, and the minimum and maximum levels were ≤10 and 410 ng/L, respectively. Fourteen (11.76%) contaminated samples had AFM₁ in concentrations in excess of the maximum levels specified in European Union regulations, i.e., 50 ng/L. The contamination ratio of milk in summer and winter months was 56.5 and 71.7%, respectively (P < 0.02). This is the first report on AFM₁ determinations in raw milk from western Iran, one of the main milk‐production areas, as well as comparison between milk obtained from different dairy farms in Iran.     

INFLUENCE OF WATER ACTIVITY, pH, HEAT TREATMENT AND PRESERVATIVE ON CHEMICAL CHANGES IN CANNED INDIAN COTTAGE CHEESE (PANEER) DURING STORAGE

ABSTRACT

Influence of water activity (A_w), pH and heat treatment on the chemical changes such as Maillard browning, oxidation and lipolysis in canned paneer has been studied by response surface methodology. Browning in canned paneer in terms of hydroxymethylfurfural content increased during storage; however, it was pH dependent. At pH above 5.0, the rate of browning decreased as A_w increased from 0.90 to 0.98. At pH below 5.0, the rate increased with increased A_w from 0.90 to 0.98. Maximum browning rates were observed at pH 5.2–5.6, low A_w values (0.90–0.92) and high heat treatment levels (up to F value 0.8). At all pH levels, increased A_w increased the oxidation rate, more so at low pH levels. Up to an F value of 0.3, heat treatment seemed to have aided the oxidation rate, but higher F values retarded the oxidation rate, more so at low A_w. Lipolysis occurred during storage, but pH had little effect on the rate of lipolysis. High A_w supported high lipolysis rates.

PRACTICAL APPLICATIONS

Raw paneer (Indian cottage cheese), popular with people in Indian subcontinent and with Indian diasporas scattered in several countries, has a shelf life of less than a day at ambient temperatures. Several attempts are being made by workers to improve the shelf life of paneer by canning process so that its market within the country and abroad improves. However, canning at usual canning time–temperatures is leading to intense chemical changes in paneer, which is not being accepted by consumers. Authors have tried to obviate such unacceptable chemical changes by reducing the intensity of canning process by adjusting so called “hurdles” of the product by hurdle technology. The present paper is a part of that attempt describing the chemical changes in paneer subjected to low heat intensity canning process with altered “hurdles.” Because the chemical changes occurring in a food product are a function of various parameters called “hurdles” like pH, water activity, heat treatment, etc., the present work attempted to identify the combination of the “hurdles” at which chemical changes are the slowest, which may find better acceptance with consumers.     

COMPOSITION,WATER-HOLDING CAPACITY AND pH OF MUSCLES FROM PIGS SUPPLEMENTED WITH PORCINE SOMATOTROPIN (pSt)1

Eighteen pigs were injected with one of three levels of recombinant porcine somatotropin (pSt) and received no more injections 7 days before slaughter. Excised triceps brachii, psoas major, semimembranosus, semitendinosus and biceps femoris muscles were analyzed for crude fat, moisture and protein contents, pH and water-holding capacity, Generally, raw muscles from somatotropin-supplemented pigs contained less crude fat than did muscles from control animals. The crude fat content of the broiled triceps brachii and roasted biceps femoris decreased in response to somatotropin supplementation. Muscles from supplemented and unsupplemented pigs did not differ in cooked muscle moisture or protein contents, raw or cooked pH or raw muscle water holding capacity.