Document Type : Research Article
Authors
Ferdowsi University of Mashhad
Abstract
Introduction: Exploiting natural substances with dual or multiple functionalities is getting more attention in food industry due to the requirement from the health- conscious consumers and the trends for sustainable environment. Hydrocolloids are high molecular weight macromolecules that can be easily dissolved and dispersed in water under appropriate conditions. They can modulate rheological properties of foods, and are generally used as food thickeners, texture modifier, stabilizers and emulsifiers for various applications. Mucilage is a high molecular weight polyuronides consisting of sugar and uronic acid units. It is partially soluble in water and can form highly viscous solution. It exhibits hampering effect on the diffusion of glucose, help to postpone the absorption and digestion of carbohydrates. The mucilage extracted from the seeds of the quince fruit contained cellulose micro-fibrils strongly associated whit a glucuronoxylan possessing a very high proportion of glucuronic acid residues. Analysis of quince seed mucilage (QSM) has shown the presence of more cellulosic fraction and hydrolysable polysaccharide.Quince seed mucilage is one of the endemic hydrocolloids, which due to high viscosity, its extraction needs a method to reduce the extraction time, energy consumption and especially raise the extraction efficiency. The traditional extraction method of polysaccharide from plant tissues are maceration, mechanical rabbling and heat reflux. Theses extraction methods depend largely on energy input and agitation to improve the solubility and mass transfer efficiency of polysaccharides. Usually, the convention extraction method requires long extraction time and high extraction temperature with low extraction yield, but high energy consumption. Ultrasound in combination with conventional extraction is a potential technique, which is a fully reproducible food process, completed in shorter time with high reproducibility, reduced processing cost, simplified manipulation and work-up. To achieve this goal, in this study ultrasound- assisted extraction (UAE) as a novel extraction method was used.
Materials andMethods:Quince seed used in this study was purchased from a local market (KhorasanRazavi, Mashhad). They were cleaned manually by removing the foreign matter such as stones, dirt and broken seeds. They were packed in hermetic plastic vessels and stored at 5ºC until further use. For mucilage extraction, first conventional extraction was optimized to select the best hydration conditions and after that UAE (24 KHz probe and 400 W power) was performed at three different levels of intensity (20, 60 and 100%) and times (5, 15 and 30 min).All chemicals used were analytical grades. Yield value of hydrocolloid was calculated by dividing the weight of dried hydrocolloid by the weight of initial dry seeds. Emulsion heat stability was determines by the method described in previous studies. In order to measuring the water absorption capacity (WAC), 0.05 g of mucilage was added to deionized water until QSM was completely wet (~ 10ml). The tubes were then centrifuged at 1600×g for 10 min. Excess water was discarded and residue was weighted. Apparent viscosity of QSM solution with 0.1% (w/v) concentration was measured using a rotational viscometer (Brookfield, DV- ІІІ, USA). Shear rate increased linearly from 2.5 - 35 s-1 at 25˚C.For measuring the foam stability and emulsion heat stability, the mucilage dispersions were prepared at 0.25 and 0.5 (w/v) respectively, and kept overnight at 4˚C. After complete hydration, 2% (w/v) egg white powder was added and then foamed by whipping at 8600 rpm for 2 min using adisperser.
Results and Discussion: Optimized conditions of conventional extraction were 45 min, 47˚C and 32.5: 1 water to seed ratio. The results showed that extraction at 30 min with 100% intensity raised the extraction yield to 42.7% in comparison with control sample.Improvement in hydrocolloid extraction by ultrasound is attributed to ultrasound pressure wave diffusion which results in cavitation phenomenon.Amplitude level and exposure time had a significant (p
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