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      Ultrasound freeze-thawing style pretreatment to improve the efficiency of the vacuum freeze-drying of okra ( Abelmoschus esculentus (L.) Moench) and the quality characteristics of the dried product

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          Highlights

          • Ultrasound freeze-thawing pretreatments improved the vacuum freeze-drying.

          • Pretreatment reduced the drying time and energy consumption.

          • Pretreatment changed the microstructure to various extent.

          • Ultrasound pretreatment retained most of the quality characteristics.

          • Pretreatment had no effect on the function groups and structure of pectin.

          Abstract

          Vacuum freeze-drying is a new and high technology on agricultural product dehydrating dry, but it faces the high cost problem caused by high energy consumption. This study investigated the effect of ultrasound (US), freeze-thawing (including the freeze-air thawing (AT), freeze-water thawing (WT), freeze-ultrasound thawing (UST), and freeze-air ultrasound thawing (AT + US)) pretreatments on the vacuum freeze-drying efficiency and the quality of dried okra. The results indicated that the application of ultrasound and different freeze-thawing pretreatments reduced the drying time by 25.0%–62.50% and the total energy consumption was 24.28%–62.35% less. The AT pretreatment reduced the time by of okra slices by 62.50% and the total energy consumption was 62.35% less. The significant decrease in drying time was due to a change in the microstructure caused by pretreatment. Besides, the okra pretreated with the US retained most of the quality characteristics (flavor, color, hardness, and frangibility) among all methods, while, AT + US had the most changeable characteristics in quality, which is deprecated in our study. The okra pretreated with the US and AT, separately, had the best dry matter content loss (9.008%, 5.602%), lower chlorophyll degradation (5.05%, 5.44% less), and higher contents of total phenolics, total flavonoids, and pectin, with strong antioxidant capacity, compared to other methods. The pretreatments did not have a large effect on the functional groups and the structure of pectin, but slightly affected the viscosity. It can be concluded that AT and US pretreatment methods are better than others.

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          Most cited references56

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          An Arabidopsis cell wall proteoglycan consists of pectin and arabinoxylan covalently linked to an arabinogalactan protein.

          Plant cell walls are comprised largely of the polysaccharides cellulose, hemicellulose, and pectin, along with ∼10% protein and up to 40% lignin. These wall polymers interact covalently and noncovalently to form the functional cell wall. Characterized cross-links in the wall include covalent linkages between wall glycoprotein extensins between rhamnogalacturonan II monomer domains and between polysaccharides and lignin phenolic residues. Here, we show that two isoforms of a purified Arabidopsis thaliana arabinogalactan protein (AGP) encoded by hydroxyproline-rich glycoprotein family protein gene At3g45230 are covalently attached to wall matrix hemicellulosic and pectic polysaccharides, with rhamnogalacturonan I (RG I)/homogalacturonan linked to the rhamnosyl residue in the arabinogalactan (AG) of the AGP and with arabinoxylan attached to either a rhamnosyl residue in the RG I domain or directly to an arabinosyl residue in the AG glycan domain. The existence of this wall structure, named ARABINOXYLAN PECTIN ARABINOGALACTAN PROTEIN1 (APAP1), is contrary to prevailing cell wall models that depict separate protein, pectin, and hemicellulose polysaccharide networks. The modified sugar composition and increased extractability of pectin and xylan immunoreactive epitopes in apap1 mutant aerial biomass support a role for the APAP1 proteoglycan in plant wall architecture and function.
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            Physicochemical change and protein oxidation in porcine longissimus dorsi as influenced by different freeze-thaw cycles.

            Effects of different freeze-thaw cycles (0, 1, 3 and 5) on physicochemical change and protein oxidation in porcine longissimus dorsi were investigated. When the number of freeze-thaw cycles increased, the thawing losses, cooking loss and b*-value increased (P<0.05), a*-value decreased (P<0.05). The cutting forces of pork increased after one cycle of freeze-thaw (from 28.3N to 40.4N) (P<0.05), but the further increase of freeze-thaw cycles would lead to decrease of cutting force. The decreases in Ca(2+)- and K(+)-ATPase activity and sulfhydryl group (P<0.05) content with concomitant increases in carbonyl content and thiobarbituric acid-reactive substances (TBARS) value (P<0.05) showed that multiple freeze-thaw could cause the porcine protein and fat oxidation, especially for the pork subjected to five freeze-thaw cycles. Gel electrophoresis patterns of porcine muscle showed that multiple freeze-thaw cycles could cause cross-linking of protein in myofibril. Overall, the freeze-thaw process has a detrimental effect on the quality of pork.
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              Comparison of different drying methods on Chinese ginger (Zingiber officinale Roscoe): Changes in volatiles, chemical profile, antioxidant properties, and microstructure.

              Nowadays, food industry is facing challenges in preserving better quality of fruit and vegetable products after processing. Recently, many attentions have been drawn to ginger rhizome processing due to its numerous health promoting properties. In our study, ginger rhizome slices were subjected to air-drying (AD), freeze drying (FD), infrared drying (IR), microwave drying (MD) and intermittent microwave & convective drying (IM&CD). Quality attributes of the dried samples were compared in terms of volatile compounds, 6, 8, 10-gingerols, 6-shogaol, antioxidant activities and microstructure. Results showed that AD and IR were good drying methods to preserve volatiles. FD, IR and IM&CD led to higher retention of gingerols, TPC, TFC and better antioxidant activities. However, FD and IR had relative high energy consumption and drying time. Therefore, considering about the quality retention and energy consumption, IM&CD would be very promising for thermo sensitive material.
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                Author and article information

                Contributors
                Journal
                Ultrason Sonochem
                Ultrason Sonochem
                Ultrasonics Sonochemistry
                Elsevier
                1350-4177
                1873-2828
                02 August 2020
                January 2021
                02 August 2020
                : 70
                : 105300
                Affiliations
                [a ]School of Food and Biological Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China
                [b ]School of Biological and Food Engineering, Chuzhou University, Chuzhou 239000, People’s Republic of China
                [c ]Department of Food Science and Nutrition, College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia
                Author notes
                [* ]Corresponding author at: School of Food and Biological Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China. cunshanzhou@ 123456163.com
                [1]

                Joint first authors.

                Article
                S1350-4177(20)30501-0 105300
                10.1016/j.ultsonch.2020.105300
                7786574
                32763750
                3209c721-c063-44bd-a80e-b99961be757d
                © 2020 Elsevier B.V.

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

                History
                : 19 March 2020
                : 7 July 2020
                : 29 July 2020
                Categories
                Original Research Article

                okra,ultrasound,freeze-thawing,vacuum-freeze drying efficiency,quality characteristics

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