Combined effect of sugar level and ice cream mix to yoghurt ratio on the quality of vanilla flavoured frozen yoghurt.

Abstract

Frozen yoghurt is a frozen dairy dessert that combines the nutritional and health benefits of yoghurt with refreshing taste and texture of ice cream. Sugar level and the ice cream mix to yoghurt ratio (ICM: Y) are among the variables affecting the quality of frozen yoghurt. At present, various levels and ratios are used resulting in different quality end products and no studies have been reported on their combined effect. The objective of the present study was to investigate the combined effect of sugar level and ICM: Y on compositional, physicochemical, physical and sensory attributes of vanilla flavoured frozen yoghurt. 33 factorial arrangement of treatments (15, 20, 25 % w/w sugar and 60:40, 70:30, 80:20 IC: Y) in a completely randomized design was used with 3 replicates. The most acceptable frozen yoghurt was compared with a market control. Parametric data were analyzed by analysis of variance (ANOVA) procedure and T-test, while sensory data was assessed by Friedman test using SPSS (ver. 25). Significant (p<0.05) interaction effect was observed in between sugar level and ICM: Y on composition except ash percentage, pH, titratable acidity (TA) and overrun while no interaction on instrumental colour, melting rate, first dripping time and complete melting time of frozen yoghurt. pH and TA were significantly (p<0.05) different among the treatments. As expected, TA decreased with decreasing yoghurt level in the ICM: Y. Increasing sugar level decreased TA with few exceptions indicating its negative effect on starter microorganisms. The overrun% was significantly (p<0.05) different among the treatments and the highest was observed in the frozen yoghurt containing 20% sugar and 70:30 ICM: Y. Melting rate showed a clear increment with the increasing sugar level and ICM: Y. Correspondingly, first dripping time and the complete melting time showed a decreasing trend. Instrumental colour was not different among treatments. The most acceptable frozen yoghurt was obtained by mixing 70:30 ICM: Y with 25% sugar, which is having 46.122.65% overrun and 1.280.41 mL/min melting rate. Compared to the control, developed frozen yoghurt had significantly (p<0.05) higher percentages of dry matter, fat and carbohydrates and significantly (p<0.05) lower percentages of protein and moisture. pH and TA of developed frozen yoghurt was significantly (p<0.05) different compared to the control. Titratable acidity of the developed frozen yoghurt was 0.39% lactic acid (LA), which is considerably lower than the control (0.72% LA). Nevertheless, it is above the acceptable minimum value prescribed for frozen yoghurt which is 0.3% LA. Lightness (L*) and yellowness (b*) of developed frozen yoghurt was significantly (p<0.05) higher compared to the control. Developed frozen yoghurt showed quick melting properties which is less desirable. Above results suggested further investigations with different IC: Y at 20 to 25% sugar level to further improve the quality of frozen yoghurt.