Mina Kargozari; Morteza Jamshid EIni
Abstract
Introduction: The osmotically dehydrated carrots can be added directly into soups, stews or can be used in a broad range of food formulations including instant soups, snack seasoning and etc. Osmotic dehydration is a suitable way to produce the shelf-stable products or partially dehydrated foods ready ...
Read More
Introduction: The osmotically dehydrated carrots can be added directly into soups, stews or can be used in a broad range of food formulations including instant soups, snack seasoning and etc. Osmotic dehydration is a suitable way to produce the shelf-stable products or partially dehydrated foods ready to place in other complementary processes such as air-drying, freezing and others. Modeling can certainly make differences in the food industry, leading to reduced costs and increased profitability. In food technology, at the simplest level, there are equations that determine the relationship between two or more variable. Simulation models in operation units and food preservation systems have attracted much attention in the past four decades. The mathematical equations describing mass transfer during osmotic dehydration, allow a better understanding of the composition of the material and operating parameters during dewatering. In this regard, many experimental and theoretical models have been reported in the literature but experimental models have more popularity because of easier applications. Regarding the classification of modeling in food processes, kinetic models are classified among theoretical models. It was ideal if we could use kinetic models based on fundamental scientific theories for the purposes of prediction and controlling the changes that occur in real food systems. But the complexity of the food makes the direct application of basic models impossible. The alternative is the direct study of kinetics on real food. As a result, the obtained models would be experimental or semi-experimental. Kinetics has developed as a powerful tool in modeling food quality features and in other words the modeling of food quality estimation is almost equivalent to the modeling of reaction kinetics in foods. The present study aimed to evaluate kinetics of osmotic dehydration of carrot cubes in terms of solid gain and water loss, which was studied at three glucose syrup concentration levels (30, 40 and 50% w/w), three salt concentration levels (5, 10 and 15% w/w) and three temperature levels of osmotic solution (30, 40 and 50°C) for 240 min. The experimental data were fitted to different semi-empirical kinetic models including Magee, Peleg and Page.
Materials and methods: Fresh well graded carrots were washed and peeled manually. A vegetable dicer was used to prepare carrot cubes of dimensions 1 cm× 1cm× 1 cm. The cubes were washed with fresh water to remove the carrot fines adhered to the surface of the fruit. The initial moisture content of the fresh carrot cubes varied from 86% to 90% (wet basis). Considering the greater effectiveness of a mixture of solutes over a single solute, a binary solution of salt and glucose syrup was used as the osmotic solution. The samples were excluded from the osmotic solution after 15, 30, 60, 120, 180 and 240 minutes. Carrot cubes were then washed with deionized distilled water, and were dried using a paper towel. Evaluation of mass exchange between the solution and sample during osmotic dehydration were made by using water loss and solid gain parameters. The experimental data were then fitted to different semi-empirical kinetic models including Magee, Peleg and Page which are widely used in biologic fields and the parameters of the models were determined. Data fitting was conducted using Microsoft Excel spreadsheet (Microsoft Office, 2010) using SOLVER add-in. Coefficient of determination (R2), chi-squared (χ2) and root mean square error (RMSE) were used to determine the best suitable model. An analysis of variance was conducted to determine the significant effects of process variables on solid gain and water loss.
Results and Discussion: At the beginning of the osmotic dehydration process, because of the high osmotic driving force between the concentrated solution and the fresh sample, the rate of water removal and solid gain was relatively high. Although water loss reached nearly the equilibrium conditions towards the late processing times, solid gain kept increasing. This increase in solid gain blocks the surface layers of the product, which reduces the concentration gradient between the product and osmotic solution, posing an additional resistance to mass exchange and lowering the rates of water loss at further processing times. It was also observed that while increasing the salt concentration, the solid gain in most of the samples significantly (p
Mina Kargozari; Leila Bagheri; Alireza Mohammadi
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. ...
Read More
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
