The effect of homogenisation, stabiliser and amylase on keeping quality of passion fruit juice

Abstract

In this study, the effects of homogenisation, stabiliser and amylase individually and in two factor combination,on the keeping quality of passion fruit juice were investigated. The juice was extracted from the two mixed types of Passiflora edulis passion fruits, sweetened, preserved with sodium metabisulphate and sodium benzoate, heated to 75°C for 15 minutes and then treated by homogenisation, stabiliser and amylase. The changes, in titratable acidity, pH, clarification/gelation, cloudiness (absorbance at 660nm), visible browning (absorbance at 20nm) viscosity flow time and concentration of total soluble solids during storage at room temperature were determined on weekly basis. Sensory qualities [colour, appearance, flavour and texture (mouth feel)] of the juice samples were also determined at the beginning and at the end of storage period on a 7-point hedonic scale. There was no clarification in all sample treatments and the untreated sample. Homogenisation (Treatment A) did not affect total titratable acidity and pH but decreased cloudiness and visible browning. Homogenisation before and after pasteurisation increased and decreased viscosity respectively. It also increased concentration of soluble materials in the juice. During storage of homogenised juice, there was no change in total titratable acidity, pH and concentration of total soluble solids but cloudness and visible browning increased whereas viscosity decreased. Stabiliser content (Treatment B) had no effect on total titratable acidity, pH, and concentration of total soluble solids. It increased cloudiness, visible browning and viscosity. There was no change in total titratable acidity, pH, viscosity and concentration of total soluble solids but the cloudiness and visible browning increased during storage. Amylase action time (Treatment C) increased total titrable acidity, cloudiness and concentration of total soluble solids. It decreased pH, visible browning and viscosity. There was no change in pH, visible browning, concentration of visible materials, cloudness and viscosity during storage. Homogenisation + stabiliser combination (Treatment D) decreased total titratable acidity, and increased cloudness, visible browning and viscosity. This combination had no effect on pH and concentration of total soluble solids. XXlll During storage of the juice which was treated with this combination, there was no change in total titratable acidity, pH and concentration of total soluble solids but there was an increase in cloudness, visible browning and viscosity during storage. Homogenisation + amylase combination (Treatment E) had no effect on total titratable acidity and pH. It decreased cloudness, visible browning and viscosity but increased concentration of total soluble solids. The total titratable acidity, cloudness and viscosity increased but there was no change an pH, visible browning and concentration of total soluble solids during storage. Stabiliser + amylase combination (Treatment F) had no effect on total titratable acidity and pH but increased cloudiness visible browning, viscosity and concentration of total soluble solids. There was a decrease in cloudness and an increase in viscosity during storage. The sensory quality scores for colour, appearance, flavour and texture of the juice indicated that among individual factor treatments, the order of preference was homogenised juice, juice with stabiliser and juice treated with amylase irrespective of the storage period. xxiv The order of preference for colour, appearance, flavour and texture in the three combinations was no the same, but the order of preference remained the same for each sensory quality attribute throughout storage time. The colour of the juice which was treated with homogenisation + stabiliser was most preferred and was followed in the order homogenisation + amylase and stabiliser + amylase combination. The appearance of the juices treated with each of the three combinations was almost the same. Homogenisation + stabiliser combination had the highest scores for flavour and was followed in the order of stabiliser + amylase and homogenisation + amylase. The texture of the juice which was treated with homogenisation + amylase combination was inferior to that of the juice which was treated with the other two combinations. Among individual factor treatments homogenisation at 3000 psi produced the best juice and among two factor combination treatments 3000 psi + 0.2% stab. treatment produced the best juice, based on the effect on the parameters measured and sensory scores. In both treatments, it is recommend to treat the juice before pasteurisation.