Effects of fermentation on the structures of yellow compounds in citrus pomace.

To enhance the stability and light resistance of the yellow compounds in citrus pomace, our study successfully isolated and purified five compounds using ultrasonic-assisted extraction and column chromatography. The identified compounds include methyl linoleate, (2-ethyl)hexyl phthalate, 1,3-distearoyl-2-oleoylglycerol, 6,6-ditetradecyl-6,7-dihydroxazepin-2(3H)-one, and n-octadeca-17-enoic acid. The monomers extracted from fresh pomace, compounds 1 and 2, exhibit structural similarities to flavonoids and carotenoids. In contrast, the polymers isolated from fermented pomace, compounds 3, 4, and 5, share structural units with the fresh pomace compounds, indicating the transformation to stable polymeric forms. This suggests that the microbial fermentation process not only enhances the value of citrus pomace, but also provides a promising pathway for the synthesis of natural antioxidant yellow pigments with far-reaching theoretical and practical significance.

Effects of different processing methods on the chlorophyll structure in kiwifruit.

Kiwifruit puree was treated with high and normal temperatures and pressures as independent variables to determinate the structural changes of chlorophyll derivatives. Two groups of colored elution samples were identified as single component compounds by High Performance Liquid Chromatography (HPLC). In addition, the structures of the two compounds were identified and analyzed by High Resolution Mass Spectrometry (HRMS) and Nuclear Magnetic Resonance (NMR). The results of HRMS and NMR demonstrate that components 1 and 2 were hydroxymethylbilane (HMB) and red chlorophyll catabolite (RCC), respectively, and indicate that HMB and RCC were the main pigments in the chlorophyll compounds after high temperature and pressure treatment. Furthermore, the cleavage pathway of the RCC in kiwifruit puree has been discussed, which provides a theoretical basis for the color protection of kiwifruit products in the course of processing.

Optimization of process parameters for naringinase production by Aspergillus tubingensis UA13 and pilot scale-up study.

To improve the naringinase production of Aspergillus tubingensis UA13, shorten the fermentation period, and verify its industrial application value, naringinase production conditions were optimized, and 5 L scale-up study in stirred tank bioreactor was carried out. Parameters, including carbon, nitrogen sources and inducer, optimal seed age, inoculum amount, temperature and pH, were adjusted and optimized in shaking flask. Keeping pH at the optimal value 6 in bioreactor, dissolved oxygen was monitored during the fermentation and the optimal stirring rate was investigated. In 5 L scale-up study, the highest naringinase activity was 72.62 U/mL, which was 1.75 times higher than that (41.52 U/mL) in shaking flask and the fermentation period was shortened by 24 h.