Effect of dairy powder rehydration state on gel formation during yogurt process

Abstract

Protein fortification and solubilisation into the milk base are important parameters enhancing yogurt texture. In this study, the milk base prepared from reconstituted skim milk powder was fortified with 2% of 'aged' (1 year old) or 'fresh' micellar casein (MC) powder. Micellar casein powders were left to rehydrate at 20°C for different times (5 or 180, 300, 480, 900 or 1440 min) before acidification with glucono-delta-lactone. The rehydration of the MC powders into milk was monitored with a granulo-morphometer equipment, thus, for the first time, allowing the elucidation of MC rehydration process into an opaque environment such as milk. Whereas the gel point was delayed proportionally to the powder rehydration length, the storage modulus appears unaffected. Besides, the gelation onset was not altered by the powder age.

Textural Properties of Acid Milk Gels: Effects of Dairy Protein Powder Rehydration State

“…Indeed, in a previous study Karam et al . () reported an increase in particle dissolution up to 70% proportionally to rehydration length. We can speculate, hence, that additional MC particles have produced further casein–casein network throughout acidification, thus resulting in a stronger gel network.…”

“…; Karam et al . ). Contrarily, MC powder present a very slow and long dispersion phase making the total rehydration process time consuming in water (Gaiani et al .…”

“…) and in complex media such as milk (Karam et al . ). Thus, the unaltered firmness, corresponding complex shear stress, syneresis and graininess values in WPI‐enriched acid milk gel samples may be due to the rapid dispersion/dissolution phase of WPI particles that usually occurs after 5 min of rehydration into milk (Karam et al .…”

“…Thus, the unaltered firmness, corresponding complex shear stress, syneresis and graininess values in WPI‐enriched acid milk gel samples may be due to the rapid dispersion/dissolution phase of WPI particles that usually occurs after 5 min of rehydration into milk (Karam et al . ). The significant increases in firmness, corresponding complex shear stress values as well as the decreases in graininess and syneresis values may be explained by the slow and progressive increase of MC powder dissolution.…”

“…Whey protein isolate (WPI) powders are known for their quick rehydration process into milk, whereas micellar casein (MC) powders are known for their long rehydration (Karam et al . ). These authors have found that MC rehydration into the milk was not totally achieved even though after 480 min of rehydration.…”