Preparation And Properties Of Polylactic Acid / Polycaprolactone / Thymeol Composite Membrane

In this study, the lactic acid bacteria stains was isolated and screened from the sour bamboo shoots (SS). The bacteria were identified as lactic acid bacteria by conventional identification methods and 16S rDNA sequencing analysis, analysed in fermentation. Antimicrobial active films based on poly(lactic acid) (PLA) were prepared with poly(ε-caprolactone)(PCL) and thymol (TH,0,3,6,9, and 12 wt%) by solvent casting methods. Properties and characterization of film were analysed. The effect of PLA/PCL/TH blend film on the microbiological and physicochemical quality of hot peppers (Capsicum frutescens var) was compared to the effects of polyethylene (LDPE) film and PLA/PCL film stored at 4±1℃ for 28 days. The reseach results are as follows:(1) There was five single strain named SSI, SS3, SS4, SS7, and SS9 were screened. The five bacteria were identified as lactic acid bacteria.The fermentation analysis showed that SS3 and SS7 strain can growth breeding and produce lactic acid quickly within 24-hour cycle, and they can grow in the condition that pH value was fall below 3.5. The calcium lactate content in fermentation broth of SS3 and SS7 were 93 g/L and 89g/L in 96-hour fermentation, respectively.(2) The films were characterized by thermal, structural, mechanical, gas barrier, and antimicrobial properties. SEM analysis revealed that the surface of film became rougher with certain porosity when TH was incorporated into the PLA/PCL blends. TH acted as plasticizers which reduce the intermolecular forces of polymer chains, thus improving the flexibility and extensibility of the films. The addition of PCL into the pure PLA film decreased the glass transition temperature of the films. The presence of thymol decreased the crystallinity of PLA phase, but did not affect the thermal stability of films. Water vapor barrier properties of films slightly decreased with the increase of TH loading. The antimicrobial properties of TH containing films showed a significant activity against Escherichia coli and Listeria monocytogenes.(3) The measured properties of hot peppers was include weight loss, color, firmness, respiration rate, vitamin C, total phenolic content, microbiological, and sensory quality. The results indicated that the package of PLA/PCL/TH film can retard the harmful change of microbiological, weight loss, anaerobic respiration, firmness, vitamin C, total phenolic content, and sensory quality. The color of hot peppers did not show significant (p<0.05) changes in all storage time. The results show that the PLA/PCL/TH film can extend the expiration date of fresh hot peppers to 21 day at 4±1℃, more effective compare with PE film.