Document Type : Research Article
Authors
1 Department of Food Science, Islamic Azad University, North Tehran Branch, Tehran, Iran.
2 Department of Food Science and Technology, Islamic Azad University, Sarvestan Branch, Sarvestan, Shiraz, Iran.
3 Department of Food Science and Technology, Islamic Azad University, Science and Research Branch, Mazandaran, Iran and Researcher of Centre for Research and Development of ETKA Organization, Iran.
Abstract
Introduction: In recent years, sugar-free or reduced-sugar foods and beverages are becoming very popular among the consumers. At the same time, consumers are increasingly concerned about the quality and safety of many products present in the diet, in particular, low-calorie synthetic or natural sweeteners. Sugar adds viscosity and provides body in drinks and semi-liquid foods like syrups and fruit juices. In order to achieve the same quality, taste and texture profile, reducing or removing sugar from a product often requires replacement with a number of alternative ingredients such as hydrocolloids. Hydrocolloids are widely used in many food formulations to improve quality attributes as thickening and gelling agents. Xanthan gum is a polysaccharide used as a food additive and rheology modifier, commonly used as a food thickening agent and a stabilizer, to prevent ingredients from separating. Stevia is an attractive natural sweetener and sugar substitute extracted from the leaves of the plant species Stevia rebaudiana. Inulin is a starchy substance found in a wide variety of fruits, vegetables, and herbs, which improves the technological properties and enhance the nutritional value of food and also has synergistic sweetening effect with sweeteners including stevia. Dietitians suggest that inulin belong to a class of water-soluble dietary fibers known as fructans, but research suggests prebiotic and bifidogenic properties of this compound that has caused it to be also regarded as a functional compound.
Materials and methods: Lemon drink with different formulations containing sugar (0, 6, 12 %), stevia (0, 0.02, 0.04 %) and xanthan (0, 0.18. 0.26 %) were prepared. To mask the bitter taste of stevia, inulin which has functional properties, was added to the formulation at the level of 0.5 %. In this study, liquid-gel method was used to suspend the solid particles of pulp and reach the desired consistency. Liquid gel structure was built by adding hot xanthan solution to the half diluted lemon drink while being stirred. Flow behavior and particle size distribution were examined. The dynamic yield stress of the samples was calculated and the stability of pulp particles in lemon drink was predicted by determination of the forces acting on the particle. Specific gravity measurement of lemon beverage was performed after removing the pulp using 50 ml pycnometer at 20°C according to the Iranian National Standard No. 2685. Mean diameter and size distribution of cloud-forming substances in pulp-free beverages were measured with a static light scattering laser diffraction-based particle size analyzer Malvern Master Sizer. Physicochemical (pH, acidity, ash, brix and density), sensory (taste and appearance) and microbial properties of lemon diet drinks were also examined.
Results and discussion: Xanthan, having considerable effect on flow behavior of lemon drink samples, created high amounts of apparent viscosity at low shear rates. In samples containing xanthan, yield stress was observed and its value was measured by extrapolation based on the Herschel-Bulkley model. The calculations of pulp suspension were conducted based on the yield stress, which were consistent with the results of stability observed. The results of the particle size distribution test showed that xanthan significantly increases the particle size of the lemon beverage. This means that the anionic hydrocolloid xanthan also react with lemon drink colloids and broader range of particle size was created. Higher xanthan concentration had led to increased particle size range. Lower sugar and stevia concentration in combination with xanthan reduced the particle size. Based on the results obtained, pH of samples ranged from 2.85 – 2.90 and acidity expressed as citric acid ranged from 0.47 – 0.52 that was in accordance with the standard related to the physicochemical properties of non-carbonated drinks and beverages (Iranian National Standard No. 2837). Other properties such as water-soluble solids value and density were not discussed due to the lack of standards for low-sugar beverages and the need for a national standard in this field was felt. The results concerned to the physical and chemical characteristics of different treatments indicated that lemon beverage acidity and pH values did not show significant differences among the samples and the samples containing higher amounts of sugar, xanthan and stevia had higher brix, ash and density values (P
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