CONICET | Buscador de Institutos y Recursos Humanos

Cheese whey is a source of food ingredients of high nutritive and functional value. It can be use directly in the formulation of foods, if it maintains a proper microbial stability. A good strategy to preserve this whey is the use of combined treatments like natural antimicrobials and low or freezing temperatures. Natural antimicrobials like nisin, Microgard and green tea have arisen as an alternative to synthetic chemicals often use in the food processing. Crioconcentration due to the freezing process could produce modifications in the physicochemical properties of the medium (pH, ionic strength and solute concentration), leading to changes in the final products. The effects of treatments in the structure modification have been analyzed for both, quality assurance and development of new products by studying the rheological behaviour of foods and ingredients. The knowledge of viscoelastic properties of whey protein suspensions is useful when specifying characteristics of foods into which are incorporated as ingredients. The objective of this study was to assess the effect of natural antimicrobials and low or freezing temperatures in the viscoelastic behaviour of whey protein suspensions. Commercial whey protein concentrate (WPC) with 37% w/w total protein was used. Suspensions were prepared with a final concentration of 9% p/v total protein and 23.6% w/v total solids. These systems were added with natural antimicrobials reaching final concentrations corresponding to the MICs obtained in previous microbiological assays (Microgard: 3% w/v; Natamicin: 300 ppm (0.3mg/ml Natamax); Nisin: 500UI/ml (0.5mg/ml Nisaplin); Green tea: an extract of 3% w/v was used as the medium for dissolving the WPC. Suspensions without adding antimicrobials were used as controls. A group of these samples was storaged at 5ºC during 14 days. Another group was frozen and maintained at -25ºC during the same period of time till melted for analysis, and the third group was analysed immediately and served as a control. Frequency scanning within the range 0.1-10 Hz at 20ºC was performed with a Haake Rheostress RS80 rheometer (Haake Instrument Inc., Paramus, N.J., USA). The elastic (G´) and viscous (G") modulus were statistically analysed for the 0.1, 1 and 10 Hz frequencies. The results obtained showed that none antimicrobial modified the mechanical spectrum characteristic of globular protein solutions, inferring that differences can be attribute only to the G" modulus. The most significant differences in the G" modulus were observed for the suspensions containing MicrogardTM. Indeed, samples kept at 5ºC showed a crossing point between G´ and G" above a frequency of 0.1 Hz. In general, refrigerated suspensions presented significantly higher values of G" for all frequencies evaluated. Data collected in this study demonstrate that adding an antimicrobial like MicrogardTM increased the viscous behaviour of frozen, refrigerated and control WPC suspensions. Additionally, keeping samples at 5ºC during 14 days produced significant changes in the viscoelastic behaviour of suspensions, demonstrated by the increases in the G" modulus.