The effect of whey protein isolate coating enriched with tyhme essential oil on trout quality during cold storage (+4 ±2 oc)

The present study, the effect of whey protein isolate (WPI) coating enriched with thyme essential oil (EO; 3, 5 and 7 %, v/v) on chemical, microbial and sensory quality of whole trout during refrigerated storage at 4±2 oC. Non-coated samples used as a control, whey protein isolate (WPI) without thyme oil (WPI0) and three different proportion of thyme EO in whey protein isolate coating solutions (WPI3, WPI5 and WPI7) were applied to whole trout. WPI coating and addition of thyme EO in WPI coating solution caused a significant decrease in initial total viable count (TVC) from 4,12 log10 CFU/g to 1,2 in WPI0, to 0,60 in WPI3, to 0,6 in WPI5 and, to 0,20 in WPI7 (p<0.05). But after three days of the storage, the TVC in control, WPI0, and WPI3 reached the same value (p>0.05), whereas the TVC in WPI5 and WPI7 were significantly lower than those of TVC (p<0.05). The upper limit of total volatile basic nitrogen value as 30 mg N/100 mg muscle and total viable counts as 6,0 log10 cfu/g at the rejection time of sensory properties were observed by six days of storage for control and WPI0 and by nine days of storage for WPI3, whereas WPI5 and WPI7 still remained at acceptable levels at the end of the storage. In conclusion, the addition of thyme EO to WPI coatings enhanced quality significantly better than that of the control and WPI coating without thyme EO during refrigerated storage, and this effect increased with increases in the thyme EO concentration in WPI coating.