Basic Research On The Application Of Cyclodextrins In Antimicrobial Food Packaging

In the present study, two application patterns of CDs in antimicrobial food packaging were investigated using the volatile and non-volatile antimicrobials. One is to prepare the antimicrobials inclusion complex with CD and then incorporate the inclusion complex directly into polymers material. In this way the antimicrobial agents could migrate and release gradually from the packaging film to the food surface. The other way is to covalent immobilization of CDs onto polymers to obtain the antimicrobial functional material by the complexation of the fixed CDs with antimicrobial agents.Allyl isothiocyanate(AITC) has strong activity in inhibiting pathogens and food spoilage bacteria. But it is difficult for AITC to be directly applied in packaging materials due to the strong volatile and the strong odor.In the present study, packaging systems that release volatile antimicrobials was simulated by entrapping AITC with CDs or fixed CDs in fabrics. The results showed that the inclusion complex of AITC with CD (CD-AITC, Molar ratio of 1:1) could be prepared with co-precipitation method and the techniques parameters was optimized by the homogeneous design. As to the index of inclusion efficiency of CDs, a simulated equation y=17.87-2.5 x₁+42.87 x₂-0.15 x₃+0.074 x₄ was obtained by MATHEMATICS4.0 Analysis and the maximum was 88.5%; As to the recovery of CDs, a simulated equation y=9.44+4 x₁+22.74x₂+0.35 x₃-0.45 x4 was obtained MATHEMATICS4.0Analysis and the maximum was 89.11%. During the experiment, an accurate quantitative analysis method of CD-AITC was developed according to the entrap and Release mechanism of CDs. The surface AITC was determined by solvent(hexane)washing and the total AITC was determined using a solvent-water extraction method on the heat condition, followed by UV spectrophotometric analysis of the concentrated extract. It has proved that the methods have advantages of little sample needed, a relatively simple operation and high accuracy. The RSD was no more than 1.26% and the average recovery of AITC was 95.6%.The formation of CD-AITC inclusion complex was confirmed by infrared spectroscopy and thermal analysis. Thermogravimetric analysis showed that the entrapped AITC had much less volatile and significantly enhanced heat-stability. Release experiments show that CD-AITC have control release characteristics and the release rate was closely related with the relative humidity (RH%) and the inclusion efficiency of CDs, which increased with the increase of RH% and slowed down correspondingly with the low inclusion efficiency of CDs. Theα- andβ-CD-AITC have similar release property, but the release rateα-CD-AITC was more slow thanβ-CD-AITC due to the spatial structure matching. The release behavior of AITC fromα- andβ-CD-AITC complexes at different RH was simulated using the Avrami equation, and the release rate constant k and the parameter n representing the release mechanism were obtained All of the n values estimated were near 0.54, which indicated that the release of included AITC in the complexes belonged to the limited diffusion kinetics. The grafting of CDs onto cellulose fiber by polyacrylic acid is a new technology and its feasibility was investigated in this paper. The results showed that the polyacrylic acid method could achieve a more satisfactory graft rate of CD than that by citric acid. The studies on reaction temperature show grafting reaction is divided into two stages, the graft of polyacrylic acid occurred in low temperature stage and CD graft mainly in the hot stage. Therefore, high temperature conditions without prejudice to the fiber quality are conducive to the fix of CD. The complexation test found that the graft amount of CDs is not entirely proportional to the AITC load of fiber due to the steric hindrance, and it was important to maintain the effective entrapping site of CD. The experimental results showed that fixed CD should be controlled between 7.5-9% while the load AITC in functional fiber obtained was 600-750uL/100g samples and the inclusion efficiency of CDs beyond up to 95%. The release behavior of the functional fibre was similar to that of CD inclusion complex, and belonged to the limited diffusion kinetics. The absorbed AITC by polyacrylic acid Network Layer didn't possess controlled release properties. Due to the steric hindrance and the AITC absorption of fiber, the AITC release rate of functional fiber is slower than unfixed CD-AITC.Since ethylparaben and benzoic acid both cannot tolerate the temperatures during polymer processing, the direct addition of the two preservatives into the packaging material would result in a great heat loss. Furthermore, their migration rate in packing materials sometimes is not satisfactory. The complexation of the two food preservative by CDs could significantly improve their thermal stability and migration behavior, and meanwhile the preparation of the corresponding antimicrobial packaging materials become possible. In this study, the solid inclusion complex of ethylparaben and benzoic acid with CD were prepared with co-precipitation method. The techniques parameters were optimized by the homogeneous design. As the index of inclusion efficiency of CDs, a simulated equation y=89.49-1.26x₁+21.34 x₂+81.15 x₃-4.42 x₄-17.57 x₂ x₃ was obtained for the benzoic acid complex and the maximum was 83.5%, a simulated equation y=2.98-0.23x₁+23.81 x₂+81.14 x₃-2.83 x₄-1.78 x₅-16.86 x₂ x₃ was obtained for the ethylparaben complex and the maximum was 83.1%, by MATHEMATICS 4.0 Analysis; As to the recovery of CDs, the simulated equation y=253.69-2.17x1-6.14 x₂+15.24 x₃-8.5 x₄ was obtained for the benzoic acid complex and y=2.24+0.37x₁+18.68 x₂+58.64 x₃-4.57 x₄+0.38 x₅-14.12 x₂ x₃ for the ethylparaben complex, the maximum values were 74.5% and 81.5%, respectively, by MATHEMATICS 4.0 Analysis. The phase solubility curve showed that both ethylparaben and benzoic acid could form inclusion complex with CD in molar ratio of 1 :1, with the complex constant K of 551 L/mol for ethylparaben and 270 L/mol for benzoic acid, which indicated that inclusion capacity of ethylparaben with CD was stronger than that of benzoic acid. The solubility of the two kind of food preservatives in water were improved by the CD complexation. The formation of the two kind of inclusion complex was also confirmed by infrared spectroscopy and thermal analysis. Thermogravimetric analysis showed that the entrapped guest had significantly enhanced heat stability.Specific migration studies were performed for both ethylparaben and benzoic using acrylate coating and polylactic acid membrane matrix filled with food simulant. The results showed that the migration behavors were influenced by the type of food stimulant. In the low-alcohol food system, both of ethylparaben and benzoic didn't migrate in polylactate acid membrane, but did in high-alcohol solution. When inclusion complexes of antimicrobials were added into the membrane, the migration had been much improved due to their impact on the membrane structure properties, and more the migration rate was also affected by the control release mechanism of cyclodextrin. In 10% or 50% ethanol solution antibacterial agents moved faster from membrane, while in 60% glycerol system the release become slow obviously and release level is very low in hexane. It could be concluded that the antimicrobial membrane with CD complexes had longer-lasting effect in low-water-activity foods.Both of ethylparaben and benzoic acid could migrate in acrylate coating with the migration quality ratio of 45-60%, which were improved once antimicrobials complex with CDs were added. The migration speed also subjected to the control release of CDs. The study indicated that such acrylic coating was not suitable for fatty food system, however could play a role in long-term antibiotics in low water activity of non-fat foods. Fickian equation could model the migration behavior of ethylparaben, benzoic acid and their CD complexes in packaging membrane. Through determination of antimicrobials migrated to food simulant at different time, Mathcad software could calculate transfer coefficient D, and the corresponding migration model was established.The CD-AITC complex and its functional fibers were used in the simulated cold meat packaging system, and showed good inhibition activity to spoilage bacteria and pathogenic bacteria. The polylactic acid film was used in Chinese sausage packaging system and showed a good bactericidal effect. These test descripted above indicated that the inclusion complex of food antimicrobials with CD and their functional materials could be applied in meat packaging for the improvement of safety and extendence of the shelf-life.