FOOD SCIENCE ›› 2021, Vol. 42 ›› Issue (3): 194-203.doi: 10.7506/spkx1002-6630-20200303-038

• Packaging & Storage • Previous Articles     Next Articles

Preparation and Characterization of Indicator Films Based on Polyvinyl Alcohol Modified by Methyl Cellulose and pH-Sensitive Dyes for Shrimp Freshness Monitoring

HUANG Jiayin, ZHOU Yaqi, CHEN Meiyu, LI Yuan, WU Tiantian, HU Yaqin   

  1. (1. National-Local Joint Engineering Laboratory of Intelligent Food Technology and Equipment, Key Laboratory of Agricultural Products Processing Technology Research, Zhejiang Province, Integrated Research Base of Southern Fruit and Vegetable Preservation Technology, Zhejiang International Cooperation Base of Health Food Manufacturing and Quality Control, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; 2. Fuli Institute of Food Science, Zhejiang University, Hangzhou 310058, China; 3. Ningbo Research Institute, Zhejiang University, Ningbo 315100, China)
  • Published:2021-02-25

Abstract: In this study, indicator films were prepared using blends of methyl cellulose (MC) polyvinyl alcohol (PVA) as film-forming materials with the addition of bromocresol purple and methyl red. The effect of substrate composition on the structure, physical properties and detection performance of indicator films was investigated, and the application in shrimp freshness monitoring was also evaluated. The Fourier transform infrared (FTIR) spectroscopy results indicated strong compatibility among the film components and the rheological studies exhibited the strongest intermolecular force when the MC-to-PVA ratio was 3:1 (m/m). The introduction of MC could enhance the properties of PVA effectively, and the film with a MC-to-PVA ratio of 3:1 (m/m) had the highest tensile strength (65.36 ± 4.29) MPa and the strongest hydrophobic properties with a water contact angle of (57.30 ± 0.81)° as well as the best light and water vapor barrier performance. All the indicator films prepared in this study could response to pH change and showed good color stability. Furthermore, when it was applied to monitor shrimp freshness under refrigeration (4 ℃), on the fourth day, the color of the indicator film with the best properties changed from reddish brown to purple brown, indicating less fresh. On the eighth day, pH and total volatile basic nitrogen (TVB-N) content were 7.73 ± 0.01 and (60.90 ± 7.00) mg/100 g, respectively, and the color turned black, indicating severe spoilage. The film color was significantly different in response to various freshness degrees, and color difference was significantly correlated with pH and TVB-N content (P < 0.05 or 0.01). Considering the indicator film could produce color change discernible to naked eyes in response to different spoilage degrees, the freshness of preserved shrimps could be graded according to the film color. Therefore, the indicator film is promising for monitoring the freshness of food products in real time.

Key words: indicator film; methyl cellulose; polyvinyl alcohol; freshness monitoring

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