Korla pear juice treated by ultrafiltration followed by high pressure processing or high temperature short time
Introduction
Korla pear (Pyrus bretschneideri rehd), commercially named korla fragrant pear, is well known for its delicate flavor, sweet taste, juicy flesh and crisp texture, which was mainly planted in Xinjiang Automonous Region of China. The yield of korla pear was 860.4 thousand ton in the year of 2013 (Xinjiang statistical bulletin) and major of korla pear was freshly consumed. Due to its special aroma and high water content (84.5–86%), it is sensitive to heat and susceptibility to mechanical injury, which caused high percentage of waste. Nowadays, few studies have been found in focusing on research and development of korla pear products (Wang and Feng, 2004, Wu et al., 2008).
Ultrafiltration (UF) membrane is able to retain large particles such as microorganism, lipids, protein and colloids; and the small particles, for example vitamins, salts, and sugars, are well reserved in juice (Cassano, Marchio, & Drioli, 2007). Compare to traditional filtration, UF is less manpower, more efficiency and shorter processing time (Echavarría, Torras, Pagán, & Ibarz, 2011), and it can avoid the use of fining agents (clarification) and high temperatures (concentration) (Baklouti, Ellouze-Ghorbel, Mokni, & Chaabouni, 2012). After or before UF, juices will undergo thermal treatment to achieve the microbial safety which can leads to detrimental changes in the sensorial and nutritional qualities of the juice (Laorko, Li, Tongchitpakdee, Chantachum, & Youravong, 2010).
High pressure processing (HPP) is a non-thermal food preservation technique which subjects foods to 100–1000 MPa at ambient temperature, and it allows inactivation of pathogenic and spoilage microorganism in foods with fewer changes in texture, color and flavor as compared to conventional technologies (Oey, Van der Plancken, Van Loey, & Hendrickx, 2008). However, low-acid fruit juices (pH > 4.6) treated by HPP at ambient temperature always have the risk of spores' germination during storage, such as Clostridium botulinum spores (http://www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/Juice/ucm072481.htm; Torres & Velazquez, 2005). Hence, to avoid the risk of spores, 4 °C should be chose as the storage temperature during the whole marketing chain (Torres & Velazquez, 2005). HPP has been successfully applied to many fruit and vegetable products and functional foods as well (Da Cruz et al., 2010); however, treatment of UF and HPP has only been found in processing of fresh apple juice (Zhao, Wang, Qiu, & Liao, 2014).
The objective of this study was to analyze the natural microorganism and quality characters of korla pear juice, in terms of clarity, color, ascorbic acid, total phenols, antioxidant capacity, and main aroma components, before and after treated by UF followed by HPP or HTST during 56 days of storage at 4 °C.
Section snippets
Preparation of korla pear juice
Korla pears were supplied by Xinjiang Top Agricultural Products Co., Ltd., Xinjiang Automonous Region, China. Fresh korla pears were sliced into small pieces (10 mm of thickness), and kept in 0.1% l-ascorbic acid before squeezed by screw juicer (GT6G7, Light Industry Machinery Factory, Zhejiang, China). The squeezed juice was centrifuged at 2063 × g for 10 min and the supernatant was collected as raw juice (pH 4.70).
UF pre-treatment
An UF unit (Nanjing Kaimi Technology Inc., Nanjing, China) with a ceramic
Effects of UF on microorganism and quality characters of korla pear juice
During UF, decrease of Qp showed deviation from linearity with a pronounced tailing (Fig. 1) due to concentration polarization phenomena and fouling of the membrane (Baklouti et al., 2012). Ceramic membrane showed a good performance during UF, with Qp value of 38.8 L/(m2h) at the stage of tailing which was 31% of the initial value.
UF effectively retained microorganism in korla pear juice with 3.05 and 3.36 log10 CFU/mL reductions of TPC and Y&M, respectively (Table 1). TSS, total sugar, pH and
Conclusion
Better preservation of main quality features, such as clarity, ΔE, ascorbic acid, total phenols, antioxidant capacity, and seven main aroma components had been found in korla pear juice treated by UF-HPP compare to UF-HTST. During 56 days of storage at 4 °C, all samples showed microbiological safety. At the end of storage, less decrease in clarity, total phenols, and capacity of antioxidant were observed in UF-HPP juice compare to UF-HTST juice. The treatment of UF followed by HPP can be an
Acknowledgement
This work was supported by the project of Recommend International Advanced Agricultural Science and Technology Plan (“948” project) of China (Project No. 2011-G20), project of National Science & Technology Support Plan of the Chinese Ministry of Education (Project No. 2011BAD39B00), and project of Novel Technologies and Equipments of Food Non-thermal Processing of the 863 High-Tech Plan of China (Project No. 2011AA100801).
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