effect of guar and basil seed gums on physical properties of low fat and light ice cream

introduction: recently, consumers have directed their interest towards low fat products as they associated them with a reduced risk of well-known health problems such as obesity and coronary heart diseases. fat is a multifunctional ingredient in ice cream system. thus, in attempts to provide desirable flavor and physical characteristics of full fat ice cream, manufactures looking for fat replacers (drake et al. 1999). hydrocolloids have functionalities such as thickening, gelling, fat replacing, which allow them to use in different industries (roller and jones, 1996; williams and phillips, 2000). guar gum is used as a stabilizer in ice cream and provides smoothness in texture, retards ice crystal growth, and increases freeze-thaw stability (wielinga, 2000). the rheological properties and potential of basil seed gum (rayhan) as a novel stabilizer for structure formation and reducer for ice recrystallization in regular ice cream have been recently investigated (hosseini-parvar, 1388; bahram-parvar, 1391). in this research, the physicalproperties of light (5% fat) and low fat (2.5% fat) ice creams as a result of replacement of milk fat by guar gum (as a commercial hydrocolloid), basil seed gum (as a novel hydrocolloid) and their blend (50:50) at different concentrations were investigated and compared to those of control sample (10% fat). materials and methods:the ice cream formulations were prepared based on the following composition: 2.5% (l), or 5% (r) or 10% (b) milk fat, 11% msnf, 15% sugar, 0.1% vanilla, 0.15% emulsifierand 0.35%, 0.45%, 0.50% or 0.55% selected gums (guar gum, basil seed gum or blend (50:50) of them). liquid materials including milk and cream were mixed together and warmed up to 50˚c. after that, the pre-weighed and mixed dry ingredients were dispersed into them, under agitation. the mixes were pasteurized at 80˚c for 25 s, homogenized at 23000 rpm for 2 min, cooled rapidly to 5˚c and then aged at constant temperature overnight (12 h) at 5˚c. the freezing was carried out in a batch soft ice cream maker. apparent viscosity of ice cream mixes were evaluated using a rotational viscometer at 5˚c and 51.8 s-1. before melting rate determination, samples were tempered at –18°c overnight, ice cream samples (30 g) were put on a wire screen mesh and allowed to melt at ambient temperature. melting rates were measured from the slop of linear portion of drained mass vs.time graphs. the ph values for mix samples were measured with a ph meter. after the mix was frozen in a batch freezer, draw temperature of ice creams was obtained using a digital thermometer.mix and ice cream samples (3 g) were diluted 1: 500 in two steps with deionized water and absorbance was measured by a spectrophotometer at 540 nm. turbidity (%) was calculated as (absorbance in mix - absorbance in ice cream)/absorbance in mix 100%. a known volume of ice cream and mix were weight and overrun was determined as (weight of the mix - weight of the ice cream)/ weight of the mix 100%. results & discussion: reducing fat in any food formulation will cause a decrease in viscosity (cody et al., 2007). fat reduction decreased apparent viscosity (p 0.05), ranging from 6.31 to 6.34. draw temperature as a measure of freezing point of ice cream is dependent on the type and concentration of the soluble constituents and varies with the composition. addition of some ingredients such as sweeteners, lactose and salts decrease the freezing point. fat is immiscible with the aqueous phase and carbohydrate polymers are very large molecules, depression of the freezing point is caused indirectly by using of these materials, as a result of decreasing the water content (marshall and arbuckle, 1996). in this study, a reduction of fat content of full fat ice cream resulted in higher draw temperature. however, there was not a specific trend in the temperature values of samples with same fat content and different fat replacer levels. there was no significant difference between turbidity of samples with same kind of gum. similar results were obtained by schmidt et al. (1993), which related to sufficient amount of milk fat (2.1 and 4.8 %), milk proteins and emulsifiers in ice cream formulations. conclution: decreasing the fat content generally caused an increase in the value of overrun. but, very high viscosity of mix may prevent vigorous agitation and air incorporation that seems the reason of why increasing fat replacer concentration resulted in overrun reduction