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.

Optimization of limonin invertase production by scaling up Aspergillus tubingensis UA13 fermentation to a 5-l scale.

The enzymatic approach is a highly effective and the major scientific method to eliminating bitter components in citrus-derived products nowadays. Microbial production of limonin invertase stands out due to its pivotal role in the removal of the bitter substance, limonin. The optimization of fermentation parameters and the study of scale-up fermentation are imperative for product commercialization. In this study, we focused on optimizing stirring speed, fermentation temperature, and initial pH to enhance the growth and limonin invertase production by the Aspergillus tabin strain UA13 in a 5-l stirred-tank bioreactor. Our results revealed the following optimal parameters are: a stirring speed of 300 rpm, a fermentation temperature of 35°C and a pH 5.0. Under these optimized conditions, the limonin invertase activity reached its peak at 63.38 U ml-1, representing a 1.67-fold increase compared to the unoptimized conditions (38.10 U ml-1), while also reducing the fermentation duration by 12 h. Furthermore, our research demonstrated that limonin invertase effectively hydrolyze limonin in grapefruit juice, reducing its content from 13.28 to 2.14 µg ml-1, as determined by HPLC, resulting in a 6.21-fold reduction of the bitter substance.

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.

Effects of lard on the formation of volatiles from the Maillard reaction of cysteine with xylose.

BACKGROUND: The presence of lipid oxidation products in the Maillard reaction pathway is of particular interest today. The objective of this study was to investigate the effect of lard and its oxidation products on the formation of volatiles from cysteine and xylose model systems. RESULTS: Headspace volatiles generated in reaction mixtures were examined by solid-phase microextraction in combination with gas chromatography-mass spectrometry. The addition of lipid had a suppressing effect on most of the sulfur-containing compounds derived from the reaction between cysteine and xylose, especially for 2-methyl-3-furanthiol, 2-furanmethanethiol, 2-methylthiophene, and 3-methylthiophene. One of the intermediates-furfural-was also formed in much lower concentration when lard was present. In addition, cysteine and xylose modified lipid oxidation pathways, so that lipid-derived alcohols, alkylfurans and aliphatic acids were formed rather than aldehydes. Compared with the lard heated alone, most aldehydes were formed at lower levels in the lard-containing reaction mixtures, and several aldehydes including hexanal, heptanal, (2E)-heptenal and (2E,4E)-heptadienal were absent. CONCLUSION: The addition of lipid was inhibitory to the formation of most sulfur-containing compounds in the Maillard reaction. Furthermore, Maillard reaction products influenced the formation of products from lipid oxidation.