Physicochemical properties and application of pullulan edible films and coatings in fruit preservation

Abstract

The effects of water, sorbitol and a sucrose fatty acid ester (SE) on the water sorption behaviour and thermal and mechanical properties of pullulan-based edible ®lms as well as the physiological responses of fruit coated with pullulan have been studied. Incorporation of sorbitol or SE in pullulan ®lms resulted in lower equilibrium moisture contents at low to intermediate water activities (a w ), but much higher moisture contents at a w > 0.75; estimates of monolayer values (within 4.1± 5.9 gH 2 O kg À1 solids) were given by application of the Brunauer±Emmett±Teller (BET) and Guggenheim±Anderson±DeBoer (GAB) models. A single glass±rubber transition (T g ), attributed to the polysaccharide component, was detected by calorimetry and dynamic mechanical thermal analysis (DMTA) at a sorbitol level of 15±30% DM. With both tests the strong plasticising action of water and polyol was evident in the thermal curves, and the T g vs moisture content data were successfully ®tted to the Gordon±Taylor empirical model. Multifrequency DMTA measurements provided estimates for the apparent activation energy of the glass transition in the range of Ä 300±488 kJ mol À1. With largedeformation mechanical testing, large decreases in Young's moduli (tensile and three-point bend tests) were observed as a result of water-and/or polyol-mediated glass-to-rubber transition of the polymeric ®lms. In the moisture content range of 2±8%, increases in¯exural modulus (E) and maximum stress (s max ) with small increases in moisture content were found for ®lms made of pullulan or pullulan mixed with 15% DM sorbitol; a strong softening effect was observed when the water content exceeded this range. Addition of sorbitol increased the water vapour transmission rate of the ®lms, whereas addition of SE had the opposite effect. Application of a pullulan/sorbitol/SE coating on strawberries resulted in large changes in internal fruit atmosphere composition which were bene®cial for extending the shelf-life of this fruit; the coated fruit showed much higher levels of CO 2 , a large reduction in internal O 2 , better ®rmness and colour retention and a reduced rate of weight loss. In contrast, similar studies on whole kiwifruits showed increased levels of internal ethylene, which caused acceleration of fruit ripening during storage.

Optimization of Extraction Condition and Characterization of Malva Verticillata Root Bark Mucilage

“…The difference in swelling and water holding capacity explains the effect of centrifugation force on capability of mucilage to bind water. Absorption of water by mucilage resulted in swelling, conformational changes and interactions between permeating water and polar groups of mucilage (Diab, Biliaderis, Gerasopoulos, & Sfakiotakis, 2001). Hydroxyl groups enable mucilage to absorb, retain and interact with water, while presence of calcium and proteins block water binding sites by forming insoluble complexes (Fedeniuk and Biliaderis, 1994).…”

PENYEDIAAN DAN PENCIRIAN HIDROGEL BERASASKAN KANJI/AKRILAMIDA DARIPADA UBI Stemona curtisii

“…Ini telah jelas menunjukkan bahawa semua bahan campur-adun yang digunakan untuk sintesis hidrogel adalah pada tahap kebolehcampuran yang baik. Menurut Diab [22] sistem polimer hidrogel yang terlarut campur dengan baik menunjukkan suhu peralihan kaca yang tunggal manakala jika suatu sistem itu tidak serasi akan mempunyai beberapa suhu peralihan kaca secara terasing yang mewakili setiap komponen dalam polimer hidrogel. Jadual 3 menunjukkan suhu peralihan kaca bagi keempat-empat jenis hidrogel yang telah disintesis.…”

Non-Conventional Tools to Preserve and Prolong the Quality of Minimally-Processed Fruits and Vegetables

“…Pullulan-based coatings have shown potential for preserving fresh strawberries and kiwifruits because of their barriers to moisture, O 2 and CO 2 [16]. Pullulan films themselves do not demonstrate antimicrobial activity [17].…”