Moisture sorption and stickiness behaviour of hydrolysed whey protein/lactose powders

Abstract

The potentially negative effects of low molecular weight disaccharides, especially lactose, on spray-drying efficiency and storage stability of dairy powders are often counterbalanced by the presence of intact milk proteins. Hydrolysis of proteins, however, may impair such protective effects and contribute to a loss in production performance. Hydrolysed or non-hydrolysed whey protein/lactose (WP/L) dispersions were spray dried, in order to examine the effects of protein hydrolysis on relaxation behaviour and stickiness of model powders. Whey proteins included a non-hydrolysed, whey protein isolate control and three hydrolysed whey protein powders (WPH), with DH values of 8, 11 and 32, where DH = degree of hydrolysis. Hydrolysis of whey proteins increased moisture sorption in WP/L powders. Moisture sorption was higher in powders containing hydrolysed proteins. Whey proteins delayed the timedependent onset of lactose crystallization, and this effect was greatest in powders containing WPH32. Glass-rubber transition (T gr) temperatures of WP/L powders were not affected by protein hydrolysis but were dominated by the lactose fraction. Powders containing hydrolysed whey proteins were more susceptible to sticking compared to intact proteins. Surface coverage by proteins or peptides was lower in powders containing hydrolysed WP, and this would have contributed to the greater susceptibility of these powders to sticking. Results suggest that hydrolysis of WP affected the relaxation behaviour of WP/L powders and altered the rate at which lactose underwent viscous flow behaviour.

Influence of protein concentration on surface composition and physico-chemical properties of spray-dried milk protein concentrate powders

“…The other powders did not crystallise due to their higher protein: lactose ratios; T gr was delayed as protein content increased, indicating delayed onset of crystallisation. This is consistent with reports that increasing the lactose content in milk powders decreases the RH at which crystallisation begins , and that the presence of high molecular weight compounds such as proteins delays the onset of crystallisation in milk powders (Jouppila & Roos, 1994). Results in Fig.…”

“…As water can only be adsorbed at the surface of a crystal, the internal water in the amorphous phase is released upon crystallisation and evaporates. Similar results were found by Jouppila and Roos (1994), who reported that lactose in SMP crystallised when the powder was stored at 66.2% RH. Pure amorphous lactose crystallises at~40% RH at 24 C (Jouppila & Roos, 1994).…”

“…Moisture sorption isotherms show the quantity of water absorbed by powders and the relative humidity (RH) at which lactose crystallises in powders. Crystallisation of non-fat powders is undesirable as it causes sticking, caking and cohesion (Jouppila & Roos, 1994). Sorption isotherms can be modelled using equations such as GuggenheimeAndersonede Boer (GAB) to determine factors such as the monolayer value of powders (Foster, Bronlund, & Paterson, 2005).…”

“…The physico-chemical properties of spray-dried dairy powders of different composition, such as milk powders with various fat levels, skimmed milk powder (SMP) with added lactose, and SMP with hydrolysed lactose or whey protein/lactose blends have been studied (Hogan & O'Callaghan, 2013;Nijdam & Langrish, 2006;Shrestha, Howes, Adhikari, & Bhandari, 2007a, 2007b. However, the effect of increasing protein content of MPCs on their physicochemical properties, such as surface composition, moisture sorption behaviour and T gr , has not yet been studied.…”

Effect of composition and drying method on glass transition temperature, water sorption characteristics and surface morphology of newly designed β-lactoglobulin/retinyl palmitate/disaccharides systems

“…Crystallization occurs time dependently when water content or temperature exceeds a critical value [25]. A number of researchers have investigated lactose [26,27] or trehalose [28] crystallization occurring in powdered mixtures during water sorption in storage.…”