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Proceeding of the 4 rd International Symposium“NEW RESEARCH IN BIOTECHNOLOGY” USAMV Bucharest, Romania, 2011Gel samples were prepared using concentrations of inulin powder (23.5–25 g), agar-agar(1.0–2.5 g) sucrose (28 g) and water (145 g).Agar-agar was swollen in cold water, and then the mixture was heated until agar-agar wasdissolved in water. Agar-agar/water solution was boiled for 5 minutes at a temperature of100 °C, and then sucrose and citric acid added to the solution. Solution was cooled down to85 °C and inulin powder was added, mixture stirred and kept for 5 minutes at thetemperature 85 °C.Subsequently, the obtained agar–agar/water with inulin powder, sugar and citric acid washot–filled in polystyrene containers (150 ml), which were covered with lids and cooleddown to 18 °C. To compare results of experimental gels the control samples were preparedusing only agar-agar or inulin powder. The analyses of the structure were carried out on thenext day after all kinds of gel samples were prepared.Gel strength (hardness)The gel strength (hardness) was characterised by cutting force. The texture was determinedby using the Texture Analyser Model TA.XT Plus (Stable Micro Systems, UK) equippedwith a load cell of 50 kg. The gel samples were positioned on a platform and cut using wirecutter (A/BC). The testing conditions were cross-head movement at a constant speed of1 mm s -1 , a trigger point of 0.09 N, distance 13 mm. The average values of tenmeasurements are reported.Preparing of microscopic samples of inulin and agar-agar powder suspended in water, andexperimental gels (Table 1)Structure of agar-agar and inulin powder dissolved in water, control gel samples with agaragar,inulin as well as gel samples with both polysaccaharides were analysed under thetriocular microscope Axioskop 40 (epifluorescence, excitation 450–490 nm, emission>500 nm). Pictures were taken by digital compact camera Canon PowerShot A620 via16 × 10 or 16 × 40 magnification of the microscope.The samples of experimental gels were cut in a 5 µm layer by device Microm HM315.Preparations were placed on a glass slide.Table 1. Recipes of the samples for analysis of microstructure and texture (g)Ingredients Samples1 2 3 4 5 6Agar 2 - 2.5 2 1.5 1Inulin - 24 23.5 24 24.5 25Water 145 145 145 145 145 145Sugar - - 28 28 28 28Citric acid - - 1 1 1 1Total 147 169 200 200 200 200Microsoft Excel software was used for the research purpose to calculate mean values andstandard deviations of the experimental data obtained in the research.72
Proceeding of the 4 rd International Symposium“NEW RESEARCH IN BIOTECHNOLOGY” USAMV Bucharest, Romania, 20113. RESULTS AND DISCUSSIONFor developing of new products that meet the people’s needs for a non-sugar diet, most ofthe foods are prepared by substituting sugar with sugar replacers – other sweeteners whichgive lower calories (sugar gives 4 kcal while fibre – 2 kcal per gram of the product)(Commission Directive 90/496/EU, Commission Directive 2008/100/EU). Jelly is a productmanufactured by cooking fruit juice with added sugar, glucose syrup and agar-agar(Figuerola, 2007).Sugar serves as a preserving agent and gelling aid. For proper structure, jelly productsrequire the correct combination of agar, sugar and glucose syrup (Tabata, 1999; Bayarri etal., 2004). In order to examine how the strength (hardness) of gel changes, the developmentof an optimum gel model is in progress without adding any extra taste, aroma or colouradditives (e.g., fruit or berry juice).Regarding the gel strength (hardness), the data of gel texture in the literature sources isinsufficient. Even very minor changes in composition or processing variables candramatically influence the textural properties of jellies (Kim et al., 2001, Matsuhashi, 1990,Panouille and Larreta-Garde, 2009). Table 2 shows the gel strength of experimental gelsamples if the content of agar-agar is decreased and the content of inulin in jellies isincreased. For example, the hardness of gel is 2.87±0.14 N (sample 1) if 2.5 g of agar–agarare added, but 0.31±0.02 N (sample 4) if 1.0 g of agar is added. The concentration of inulinpowder was in the range from 23.5 to 25 g 100 g -1 in gel mix.Table 2. Gel strength of experimental samplesSample no Amount of agar-agar, g 100 g -1 Gel strength, N1 2.5 2.87 ± 0.142 2.0 2.38 ± 0.123 1.5 0.96 ± 0.054 1.0 0.31 ± 0.02In this case the gel strength is a strong function of agar-agar concentration in gels. Thestrength of experimental gels decreases with increase in the content of inulin in gels. Incomparison with agar-agar gel, the mixed gels were more easily deformable and they hadlower strength. The significance of these interactions could influence the functionality ofagar-agar in jellies. The type of inulin powder used in experiment, and its concentration didnot form stable gel. More concentrated samples with inulin powder (50 and 60 g 100 g -1 )have to be prepared for formation harder gels (Chiavaro et al., 2007).Figure 1 and Figure 2 show the microscopic images of particle size of inulin and agar-agarpowder suspended in water and experimental gels. Agar can form either transparent oropaque gels which are thermally reversible on heating and cooling (McClements, 2007).Inulin with a crystal structure undergoes dispersion and forms a suspension in a waterenvironment at room temperature. Most of the crystals do not change their structure. Thecrystals which do not dissolve form a weak three-dimensional network which isstrengthened by dissolved inulin (Glibowski and Pikus, 2011). Obtained results showed thatafter heating and cooling the agar–agar is swollen and it formed the gel structure The73
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