Peter Aldred

Denaturation and Physical Characteristics of Spray-Dried Whey Protein Isolate Powders Produced in the Presence and Absence of Lactose, Trehalose, and Polysorbate-80

The denaturation (loss of protein through aggregation and/or change in secondary structure) and physical characteristics such as powder morphology, particle size and size distribution, amorphous/crystalline behavior, and solubility of whey protein isolate (WPI) were investigated in a spray-drying process. The protective efficacy of sugars (lactose and trehalose) and low-molecular-weight surfactant polysorbate-80 (Tween-80) on the secondary structure (β-turn, β-sheet and α-helix) and physical characteristics of spray-dried WPI was quantified. The WPI, WPI+sugar, and WPI+Tween-80 formulations were spray dried maintaining the total solids at 10% (w/w). The inlet and outlet temperatures were maintained at 180 and 80°C, respectively. The results showed that the loss of protein through denaturation and aggregation was not significant (p > 0.05). However, a significant (p < 0.05) alteration of the secondary structural elements was observed. Due to spray drying of WPI without protectants, the β-sheet and β-turn were decreased by 4.4 and 14.5%, respectively, and the random coil increased by 20.7%. The α-helix of WPI remained unaltered during the spray-drying process. The presence of Tween-80 effectively protected the α-helix and β-sheet but the β-turn remained vulnerable and was decreased. No significant (p > 0.05) change in the solubility of WPI was observed due to spray drying. Spray drying of WPI+sugar produced essentially amorphous particles. The dried powder particles were spherical with wrinkled or folded surface.

Pathogens in Beer

Pathogenic (disease-causing) microorganisms cannot survive in beer due to the presence of various inhibitory factors/hurdles. The major intrinsic hurdles that a pathogen must overcome to survive in a beer are the presence of ethanol produced by yeasts during fermentation (up to 10% (v/v), typically 3.5–5.0% (v/v)), hop (Humulus lupulus) bittering compounds (approx. 17–55 parts per million iso-α-acids), low pH (approx. 3.9–4.4), carbon dioxide (approx. 0.5% (w/w)), low oxygen (<0.1 ppm), and the lack of nutritive substances. Ethanol and hops interfere with essential cell membrane functions, the low pH hinders enzyme activity, the lack of nutrients and oxygen starves many potential pathogens, whilst elevated dissolved carbon dioxide lowers the pH, inhibits enzymes, affects cell membranes, and creates an anaerobic environment. In addition to these intrinsic factors, many stages of the brewing process reduce the potential for contamination, such as mashing, wort boiling, pasteurization, filtration, aseptic packaging and cold storage. Various studies have shown that the survivability of pathogens such as Escherichia coli, Salmonella Typhimurium, and Vibrio cholerae in most beers is very poor. However, beers without, or with, reduced levels of one or more of these antimicrobial “hurdles” are more prone to the survival and/or growth of pathogenic organisms. Examples are low-alcohol and unpasteurized beer, for which special attention must be paid to ensure their safety.