Review: Technology, Chemistry and Microbiology of Whey Cheeses

In whey cheese manufacture, whey, plain or added with milk, is heated by direct fire, bubbling steam or alternatively in jacketed vats. In some cases, salt s or organic acids are previously added. At 80-85 OC, the first particles of curd form; at 85-95 'C, the curd may be cooked for a few minutes to reduce moisture content and/or to obtain the desirable level of browning. After drainage at room temperature during molding for ca. 4 h, whey cheese is stored at ca. 4 'C. The typical mass yield is 6%, but addition of milk, calcium salts and preliminary concentration of protein (by condensation or ultrafiltration techniques) may increase yield considerably. Some types of whey cheeses are supposed to be consumed within a short time upon manufacture (e.g., Ricotta, Requeijdo and Manouri), whereas others bear a longer shelf life (e.g., Gjetost, Mysost and Myzithra). Whey cheeses are significantly different from one another in terms of chemical composition, which is mainly due to variations in the source and type of whey, as well as to the processing practices followed. Moisture content and pH of whey cheeses are usually high and favor microorganism growth (molds, yeasts, lactic acid bacteria and Enterobacteriaceae account for the dominant microflora in these cheeses). Adequate packaging of whey cheeses should be provided, and legislation should be prepared to fix standard characteristics of each type of whey cheese, and hence protect typical products from adulteration and fakes. Marketing efforts should also be aimed at increasing whey cheese consumption, either directly or incorporated in desserts, snack dips and pasta-type dishes

Characterization of requeijão and technological optimization of its manufacturing process

In attempts to characterize Portuguese whey cheese (Requeijão) and optimize the manufacture thereof I7 whey cheeses were produced according to a factorial design using heating time, heating temperature and fractional addition of ovinelcaprine milk as manipulated technological variables. Chemical analyses were carried out for the 17 cheeses, whereas sensorial and rheological analyses were carried out for eight selected whey cheeses and a reference (i.e. a whey cheese produced locally according to traditional procedures). A true local maximum exists for moisture content (at a temperature of about 93°C heating time of about 30 min and addition of about 17% ovine milk) which lies well within the range chosen for experimentation. Fat content of Requeijão was positively affected by heating temperature (especially via its quadratic effect) and, to a lesser extent, by heating time (especially via its linear effect); nitrogen content was especially affected by heating temperature (via its quadratic effect); and moisture content was affected especially by heating temperature (via its quadratic effect). The sensorial analyses showed that the eight whey cheeses produced were prefered with respect to the reference whey cheese. For rheological analyses the most significant observations pertain to the high strain dependence of the dynamic moduli, absence of a true equilibrium storage modulus, and relatively low difference between the loss and the storage modulus

Mechanical behaviour of heavily compacted bentonite under high suction changes

The paper reports the results of an experimental study carried out on a bentonite compacted to a dry density of up to 1·7 Mg=m3, a high value for this type of soil. The soil fabric has been studied using a variety of techniques, revealing a clear bimodal pore distribution that corresponds to two distinct structural levels: a microstructural one and a macrostructural one. The main testing programme has been performed using oedometers especially designed to apply a very large range of suctions. By applying the axis-translation technique (using nitrogen as the gas fluid), it has been possible to reach suctions up to 15 MPa. The higher suction range has been achieved by applying a controlled atmosphere where the relative humidity has been fixed by a solution of sulphuric acid or salts. In this way suctions up to 550 MPa could be reached. The maximum vertical stress that could be applied in the apparatus was 10 MPa. Two types of test have been carried out: (a) tests in which a combination of loading paths at constant suction and drying/wetting paths at constant load were applied; (b) swelling tests under constant-volume conditions in order to determine the swelling pressure and the stress path followed during wetting. The results of the experimental programme are examined, taking into account the role of the soil fabric in controlling observed mechanical behaviour. In addition, the results of the laboratory tests are reproduced and interpreted using a generalised plasticity model that considers explicitly the interaction between macrostructure and microstructure. In this way, it is possible to achieve a more complete understanding of the mechanisms that underlie observed behaviour, and in particular the interplay between the two structural level

Optimisation, by response surface methodology, of degree of hydrolysis and antioxidant and ACE-inhibitory activities of whey protein hydrolysates obtained with cardoon extract

The hydrolysis of bovine whey protein concentrate (WPC), alpha-lactalbumin (alpha-La) and caseinomacropeptide (CMP), by aqueous extracts of Cynara cardunculus, was optimized using response surface methodology. Degree of hydrolysis (DH), angiotensin-converting enzyme (ACE)-inhibitory activity and antioxidant activity were used as objective functions, and hydrolysis time and enzyme/substrate ratio as manipulated parameters. The model was statistically appropriate to describe ACE-inhibitory activity of hydrolysates from WPC and alpha-La, but not from CMP. Maximum DH was 18% and 9%, for WPC and alpha-La, respectively. 50% ACE-inhibition was produced by 105.4 (total fraction) and 25.6 mu g mL(-1) (<3 kDa fraction) for WPC, and 47.6 (total fraction) and 22.5 mu g mL(-1) (<3 kDa fraction) for alpha-La. Major peptides of fractions exhibiting ACE-inhibition were sequenced. The antioxidant activities of WPC and alpha-La were 0.96 +/- 0.08 and 1.12 +/- 0.13 mmol trolox equivalent per mg hydrolysed protein, respectively.info:eu-repo/semantics/acceptedVersio