The effect of different concentrations of gum tragacanth on the textural characteristics of low-fat Iranian White cheese was studied during ripening. A batch of full-fat and 5 batches of low-fat Iranian White cheeses with different gum tragacanth concentrations (without gum or with 0.25, 0.5, 0.75, or 1 g of gum/kg of milk) were produced to study the effects of fat content reduction and gum concentration on the textural and functional properties of the product during ripening. Cheese samples were analyzed with respect to chemical, color, and sensory characteristics, rheological parameters (uniaxial compression and small-amplitude oscillatory shear), and microstructure. Reducing the fat content had an adverse effect on cheese yield, sensory characteristics, and the texture of Iranian White cheese, and it increased the instrumental hardness parameters (i.e., fracture stress, elastic modulus, storage modulus, and complex modulus). However, increasing the gum tragacanth concentration reduced the values of instrumental hardness parameters and increased the whiteness of cheese. Although when the gum concentration was increased, the low-fat cheese somewhat resembled its full-fat counterpart, the interaction of the gum concentration with ripening time caused visible undesirable effects on cheese characteristics by the sixth week of ripening. Cheeses with a high gum tragacanth concentration became very soft and their solid texture declined somewhat.

The effect of whey protein concentrate (WPC) and gum tragacanth (GT) as fat replacers on the chemical, physical, and microstructural properties of nonfat yogurt was investigated. The WPC (7.5, 15, and 20 g/L) and GT (0.25, 0.5, 0.75, and 1 g/L) were incorporated into the skim milk slowly at 40 to 45 degrees C with agitation. The yogurt mixes were pasteurized at 90 degrees C for 10 min, inoculated with 0.1% starter culture, and incubated at 42 degrees C to pH 4.6, then refrigerated overnight at 5 degrees C. A control nonfat yogurt and control full fat yogurt were prepared as described, but without addition of WPC and GT. Increasing amount of WPC led to the increase in total solids, total protein, acidity, and ash content, whereas GT did not affect chemical parameters. Increasing WPC caused a more compact structure consisting of robust casein particles and large aggregates. Firmness was increased and susceptibility to syneresis was decreased as WPC increased. No significant difference was observed for firmness and syneresis of yogurt fortified with GT up to 0.5 g/L compared with control nonfat yogurt. Increasing the amount of gum above 0.5 g/L produced softer gels with a greater tendency for syneresis than the ones prepared without it. Addition of GT led to the coarser and more open structure compared with control yogurt.

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The goal of this study was to evaluate quality changes during deep fat frying of five cultivars of sweet potato (Ipomoea batatas L.

Background: Sweet potato (Ipomoea batatas L.) is a very rich source of starch. There is increased interest in starch digestibility and the prevention and management of metabolic diseases.Objective: The aim of this study was to evaluate the levels of starch fractions and predicted glycemic index of different cultivars of sweet potato.Material and Method: French fries produced from five cultivars of sweet potato (‘Ginseng Red’, ‘Beauregard’, ‘White Travis’, ‘Georgia Jet clone #2010’ and ‘Georgia Jet’) were used. The level of total starch (TS), resistant starch (RS), digestible starch (DS), and starch digestion index starch digestion index in the samples were evaluated. In vitro starch hydrolysis at 30, 90, and 120 min were determined enzymatically for calculation of rapidly digestible starch (RDS), predicted glycemic index (pGI) and slowly digestible starch (SDS) respectively. Results: The RS content in all samples had an inversely significant correlation with pGI (-0.52; P<0.05) while RDS had positive and significant influence on both pGI (r=0.55; P<0.05) and SDI (r= 0.94; P<0.01). ‘White Travis’ and ‘Ginseng Red’ had higher levels of beneficial starch fractions (RS and SDS) with low pGI and starch Index (SDI), despite their higher TS content. Generally, all the cultivars had products with low to moderate GI values. Conclusion: The glycemic index of these food products highlights the health promoting characteristics of sweet potato cultivars.Keywords: Sweet potato, Ipomoea batatas L, French fries, in vitro starch digestibility, glycemic index, resistant starch

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