Study of different barriers to microbiology stabilization of goat and sheep whey and impact on the physicochemical properties and physical stability of products

Abstract

Goat cheese whey (GCW) and sheep cheese whey (SCW) are byproducts of cheese production and are usually discarded. To create alternatives for the use of this waste, it is necessary to stabilize it microbiologically. Initially, the kinetic parameters of microbial inactivation in GCW were evaluated. It was verified that the inactivation followed a first order kinetics, being established values of D from 65.7 to 1.2 minutes in temperatures of 62 to 75oC, respectively. Three binomials were selected to evaluate the microbiological and physical-chemical characteristics of the whey, with and without added sugar, during storage at 7oC. It was observed that the binomial 75oC/5 min ensured the microbiological stability of the whey for up to 21 days, regardless of the addition of sugar, with less effect on physical stability when compared to the more severe binomials (80oC/1 min). Thus, to increase the shelf life of the whey, other barriers were necessary. In this way, the effects of the association of heat treatment with fermentation were studied, including the impact of the addition of protease and the use of ultrasound during fermentation. It was found that the fermentations under ultrasound showed a higher rate of pH reduction in the GCW (23-32%). Physical stability evaluation showed that both products had cream separation (up to 60%) and translucent whey formation (up to 80%). For antioxidant activity, an increase of 40% (SCW) and 30% (GCW) was observed, compared to unfermented whey. For lactic bacteria (LAB) counts, there was a reduction during storage (1.5-3.0 log CFU.mL -1 ). Thus, the results demonstrated that the source/composition of whey, mainly fat content, affected the destabilization rate and loss of viability of LAB, caused by nutrient depletion and poor tolerance at pH ~4.0. Finally, the efficacy of nisin, addition of Lacticaseibacillus casei as a bioprotective culture and direct acidification with lactic acid (up to pH 4.5, 3.5 and 2.5) were evaluated as tools to guarantee the stability of GCW and SCW during 28 days at 7°C. Nisin and acidification at pH 3.5 and 2.5 maintained total and psychrotrophic bacteria counts below 1 log CFU.mL -1 , with pH and acidity stable during sample storage. Inoculation with L. casei was also effective, reaching 7-8 log CFU.mL -1 and protecting the samples with mild (SCW) or no acidification (GCW) of the samples. Regarding physical stability, all samples were destabilized, but those acidified at pH 3.5 and 4.5 had greater cream and sediment formation. On the other hand, the particle size data showed little difference between the samples (0 and 28 days), suggesting that shaking the whey was able to resuspend the separated particles during static storage. Therefore, a general evaluation of the results indicates that the best solutions for stabilizing GCW and SCW are the thermal treatment of 75oC/5min associated with antimicrobial (nisin) and bioprotective culture (L. casei); even so, if it is necessary to guarantee the physical stability of the whey in the developed product, it is important that additional strategies be studied, such as the use of stabilizers and skimming, especially for acidic products. The data obtained in this study foster new perspectives regarding the use of GCW and SCW for the development of new dairy products, aiming to promote an increase in the income of rural producers and reduce environmental impacts. Keywords: Goat cheese whey. Sheep cheese whey. Heat treatment. Ultrasound. Protease. Antimicrobial. Bioprotection. Product development.