Effect of in vitro digestion and fermentation of kiwifruit pomace polysaccharides on structural characteristics and human gut microbiota.

Kiwifruit pomace is abundant in polysaccharides that exhibit diverse biological activities and prebiotic potential. This study delves into the digestive behavior and fermentation characteristics of kiwifruit pomace polysaccharides (KFP) through an in vitro simulated saliva-gastrointestinal digestion and fecal fermentation. The results reveal that following simulated digestion of KFP, its molecular weight reduced by 4.7%, and the reducing sugar (CR) increased by 9.5%. However, the monosaccharide composition and Fourier transform infrared spectroscopy characteristics showed no significant changes, suggesting that KFP remained undigested. Furthermore, even after saliva-gastrointestinal digestion, KFP retained in vitro hypolipidemic and hypoglycemic activities. Subsequently, fecal fermentation significantly altered the physicochemical properties of indigestible KFP (KFPI), particularly leading to an 89.71% reduction in CR. This indicates that gut microbiota could decompose KFPI and metabolize it into SCFAs. Moreover, after 48 h of KFPI fecal fermentation, it was observed that KFPI contributed to maintaining the balance of gut microbiota by promoting the proliferation of beneficial bacteria like Bacteroides, Lactobacillus, and Bifidobacterium, while inhibiting the unfavorable bacteria like Bilophila. In summary, this study offers a comprehensive exploration of in vitro digestion and fecal fermentation characteristics of KFP, providing valuable insights for potential development of KFP as a prebiotic for promoting intestinal health.

Effects of kiwi fruit (Actinidia chinensis) polysaccharides on metabolites and gut microbiota of acrylamide-induced mice.

Introduction: Kiwifruit (Actinidia chinensis) has rich nutritious and medicinal properties. It is widely consumed worldwide for the intervention of metabolism disorders, however, the underlying mechanism remains unclear. Acrylamide, a well-known toxic ingredient, mainly forms in high-temperature processed carbohydrate-rich food and causes disorders of gut microbiota and systemic metabolism. Methods: This study explored the protective effects and underlying mechanisms of kiwifruit polysaccharides against acrylamide-induced disorders of gut microbiota and systemic metabolism by measuring the changes of gut microbiota and serum metabolites in mice. Results: The results showed that kiwifruit polysaccharides remarkably alleviated acrylamide-induced toxicity in mice by improving their body features, histopathologic morphology of the liver, and decreased activities of liver function enzymes. Furthermore, the treatment restored the healthy gut microbiota of mice by improving the microbial diversity and abundance of beneficial bacteria such as Lactobacillus. Metabolomics analysis revealed the positive effects of kiwifruit polysaccharides mainly occurred through amino and bile acid-related metabolism pathways including nicotinate and nicotinamide metabolism, primary bile acid biosynthesis, and alanine, aspartate and glutamate metabolism. Additionally, correlation analysis indicated that Lactobacillus exhibited a highly significant correlation with critical metabolites of bile acid metabolism. Discussion: Concisely, kiwifruit polysaccharides may protect against acrylamide-induced toxicity by regulating gut microbiota and metabolism.

Self-Paced Broad Learning System.

Broad learning system (BLS), an efficient neural network with a flat structure, has received a lot of attention due to its advantages in training speed and network extensibility. However, the conventional BLS adopts the least square loss, which treats each sample equally and thus is sensitivity to noise and outliers. To address this concern, in this article we propose a self-paced BLS (SPBLS) model by incorporating the novel self-paced learning (SPL) strategy into the network for noisy data regression. With the assistance of the SPL criterion, the model output is used as feedback to learn appropriate priority weight to readjust the importance of each sample. Such a reweighting strategy can help SPBLS to distinguish samples from "easy" to "difficult" in model training, equipping the model robust to noise and outliers while maintaining the characteristics of the original system. Moreover, two incremental learning algorithms associated to SPBLS have also been developed, with which the system can be updated quickly and flexibly without retraining the entire model when new training samples are added or the network needs to be expanded. Experiments conducted on various datasets demonstrate that the proposed SPBLS can achieve satisfying performance for noisy data regression.

Formation of odorous aldehydes, nitriles and N-chloroaldimines from free and combined leucine during chloramination.

Amino acids (AAs) are a major group of odorous disinfection by-product (O-DBP) precursors. O-DBPs formations during free chlorine disinfection has been previously investigated. However, knowledge regarding the O-DBP formation mechanism and kinetics under chloramination of AAs is very limited. In this study, the generation of odorous isovaleraldehyde, isovaleronitrile and N-chloroisovaleraldimine from leucine (Leu), a typical and abundant AA in many drinking water sources, in its free and combined forms during chloramination under several typical addition schemes of disinfectants was investigated. Free Leu and glycylleucine (Gly-Leu) were chosen as model compounds since they have been indicated to be O-DBP precursors during chlorination. Intermediate product analysis and kinetics studies were conducted to study the reaction mechanisms. Impacts of disinfectants dosages and pH were also investigated in experiments and simulations. The results indicated that comparing with chlorination, chloramination of Leu has its uniqueness by participating in reacting with isovaleraldehyde to form N-chloroisovaleraldimine. And all the three O-DBPs formations from free Leu and Gly-Leu during chloramination (with preformed NH2Cl) were less than those during chlorination, indicating that using NH2Cl for disinfection ensures control over the off-flavor problems to some degree. When chloramination was realized by adding chlorine and ammonia separately, a longer pre-chlorination time led to greater yields of the O-DBPs from both precursors, whereas adding ammonia before chlorine promoted more isovaleraldehyde formation from free Leu. Under alkaline conditions, more isovaleronitrile and N-chloroisovaleraldimine were produced, and acidic conditions led to more isovaleraldehyde formation during chloramination. Notably, O-DBPs yields from free Leu were approximately 1000 times greater than those from Gly-Leu during chloramination under all the schemes. In addition, chlor(am)ination experiments with real water from Taihu Lake (the third largest freshwater lake and water source for twenty million people in China) indicated the formation of N-chloroisovaleraldimine and isovaleraldehyde was highly likely to cause odorous problems in drinking water. This study facilitates further understanding of the causes of off-flavor issues in drinking water and can help control the odorous problems by optimizing the operating parameters of drinking water treatment plants.

Formation of odorous aldehydes, nitriles and N-chloroaldimines from combined leucine in short oligopeptides during chlorination.

Previous studies have focused on investigating the formation of odorous by-products during the chlorination of free amino acids (AAs). However, studies on the formation of odorous by-products during the chlorination of combined AAs, which are much more abundant in natural waters than free AAs, are very limited. In this study, the generation of odorous aldehyde, nitrile and N-chloroaldimine from short oligopeptides containing combined Leucine (Leu) (a typical precursor of odorous by-products), including glycylleucine (Gly-Leu), leucylglycine (Leu-Gly), and trileucine (Leu-Leu-Leu), was investigated. The reaction mechanisms were then proposed based on Acquity UPLC-qTOF mass spectrometer measurement and kinetic studies modelled with Kintecus. The results indicated that a series of sequential reactions, including substitution, dehydrohalogenation, ß-elimination, hydrolysis and decarboxylation reactions, occurred during the chlorination of short oligopeptides. The chlorination of Gly-Leu and Leu-Leu-Leu formed free Leu, which continued to react with chlorine, producing isovaleraldehyde, isovaleronitrile and N-chloroisovaleraldimine. Compared with Gly-Leu, Leu-Leu-Leu produced less free Leu, and therefore, a smaller amount of Leu-derived odorous by-products was generated. Leu-Gly produced free Gly, which was not a precursor of odorous by-products. Thus, neither isovaleraldehyde nor N-chloroisovaleraldimine was formed. Notably, isovaleronitriles can be formed directly from a ß-elimination reaction during chlorination of Leu-Gly and Leu-Leu-Leu, and thus high yields of isovaleronitriles were observed after chlorination. The yields of odorous by-products during chlorination of short oligopeptides increased with increasing Cl/N ratios (the molar ratio of chlorine to nitrogen in the AAs) and reached their maximum at Cl/N = 2.4, except the yield of isovaleraldehyde formed from Gly-Leu reached its maximum at Cl/N = 1.6. UV and UV/H2O2 pre-treatments decreased odorous by-product formation during subsequent chlorination through non-peptide bond breaking of short oligopeptides. This study facilitates the identification of the causes of off-flavour problems in drinking water and the development of ways to control these problems.

Formation of odorous by-products during chlorination of major amino acids in East Taihu Lake: Impacts of UV, UV/PS and UV/H2O2 pre-treatments.

Certain amino acids (AAs) can form odorous aldehydes, nitriles and N-chloroaldimines during chlorination. Ultraviolet (UV) photolysis, ultraviolet/persulfate (UV/PS) and ultraviolet/hydrogen peroxide (UV/H2O2) treatments have been reported to decrease trace organic contaminants in drinking water. In this study, 20 common AAs in East Taihu (ET) Lake (the main drinking water source for the surrounding cities) were determined during one year (four seasons). The impacts of UV photolysis alone and two UV-advanced oxidation process (AOP) pre-treatments on the formation of aldehydes, nitriles and N-chloroaldimines during post-chlorination of water containing three of the most detected AAs (i.e. valine (Val), leucine (Leu) and isoleucine (Ile)) in ET Lake were investigated. Results showed that the two UV-AOPs significantly decreased the odorous by-product formation from AAs compared with UV photolysis alone. The formation of N-chloroaldimines was more easily controlled than that of aldehyde and nitrile. Furthermore, UV/H2O2 was more effective than UV/PS at pH = 5 and 7. At pH = 9, the two UV-AOPs had similar effects and did not perform very well. In addition, the UV-AOPs controlled the formation of odorous by-products effectively at Cl/AA (molar ratio of chlorine to amino acid) ratios of 2.4 and 3.0 but increased their formation at Cl/AA ratios of 0.8 and 1.2. Experiments in real water showed that UV/H2O2 was more suitable for controlling the off-flavor problem caused by chlorination of AAs in ET Lake.