A review on natural sweeteners, sweet taste modulators and bitter masking compounds: structure-activity strategies for the discovery of novel taste molecules.

Growing demand for the tasty and healthy food has driven the development of low-calorie sweeteners, sweet taste modulators, and bitter masking compounds originated from natural sources. With the discovery of human taste receptors, increasing numbers of sweet taste modulators have been identified through human taste response and molecular docking techniques. However, the discovery of novel taste-active molecules in nature can be accelerated by using advanced spectrometry technologies based on structure-activity relationships (SARs). SARs explain why structurally similar compounds can elicit similar taste qualities. Given the characterization of structural information from reported data, strategies employing SAR techniques to find structurally similar compounds become an innovative approach to expand knowledge of sweeteners. This review aims to summarize the structural patterns of known natural non-nutritive sweeteners, sweet taste enhancers, and bitter masking compounds. Innovative SAR-based approaches to explore sweetener derivatives are also discussed. Most sweet-tasting flavonoids belong to either the flavanonols or the dihydrochalcones and known bitter masking molecules are flavanones. Based on SAR findings that structural similarities are related to the sensory properties, innovative methodologies described in this paper can be applied to screen and discover the derivatives of taste-active compounds or potential taste modulators.

Metabolomic Analysis Provides New Insight Into Tolerance of Huanglongbing in Citrus.

There have been efforts to develop citrus cultivars that are tolerant of Huanglongbing (HLB), a catastrophic phloem-limited disease. Previous studies demonstrated that continuous plant growth with phloem regeneration is one of the major characteristics of HLB tolerance. In this study, the metabolic mechanisms of HLB tolerance in citrus were elucidated using a multiple pathway-targeted metabolomic approach. Comparative analysis of healthy and infected HLB-tolerant and HLB-sensitive mandarin cultivars (Citrus reticulata) revealed differentially expressed metabolic responses among different groups. Pathway enrichment analysis indicated aspartate and glutamate metabolism, purine metabolism, and biosynthesis of plant hormones were upregulated in the tolerant group, except salicylic acid signaling. Catabolic pathways linked to energy-yielding metabolism were also upregulated in the tolerant group. These metabolisms and pathways were interconnected with each other, unveiling a pivotal metabolic network associated with HLB tolerance. In the network, auxins and cytokinins, the plant hormones responsible for plant growth and phloem regeneration, were accumulated. In addition, purine metabolites serving as energy carriers and nitrogen sources of plants were increased. Only salicylic acid-related metabolites for plant defense responses were decreased in the tolerant group. Our findings may evidence the strategy of HLB-tolerant cultivars that sustain plant growth and phloem formation rather than displaying direct plant defense to overcome the disease.

Phytochemical profiles, and antimicrobial and antioxidant activities of greater galangal [Alpinia galanga (Linn.) Swartz.] flowers.

Previous studies of galangal (Alpinia galanga) have focussed mostly on rhizomes but seldom on flowers. A comprehensive look at galangal flowers could reveal additional benefits. The chemical composition of galangal flowers was significantly (p < 0.05) different from that of galangal rhizome. Pentadecane and α-humulene were identified as major compounds of galangal flower essential oil. 1'-acetoxyeugenol acetate was identified as the highest compound in flowers and exhibited the strongest antimicrobial activity among all fractions, with MIC50 values of 34 µg/ml against Staphylococcus aureus and 68 µg/ml against Listeria monocytogenes. Galangal flowers had a 3-fold higher total phenols content than had rhizomes (10.5 vs. 3.33 mg GAE/g powder). The antioxidant activities of different flower fractions varied from 2 to 4.45 mmol  trolox/g phenolics. These findings suggest that antimicrobial and antioxidant agents extracted from galangal flowers could potentially be utilized as natural food preservatives or as therapeutic agents.

Optimal immobilization of Beta-glucosidase into chitosan beads using response surface methodology

Background: β-Glucosidase is known as an effective catalyst for the hydrolysis of various glycosides and immobilization is one of the most efficient strategies to improve its activity recovery and properties. Results: Crosslinking-adsorption-crosslinking method was employed to immobilize β-glucosidase into chitosan beads and response surface methodology (RSM) was used to optimize the immobilized conditions of the maximum activity recovery. Enzyme concentration and adsorption time were found to be significant influence factors, and the maximum activity recovery (50.75%) obtained from response surface methodology was in excellent agreement with experimental value (50.81%). Furthermore, various characteristics of immobilized β-glucosidase were evaluated. Compared to the free β-glucosidase, the immobilized enzyme exhibited broader pH and temperature ranges, enhanced thermal stability, better storage stability and reusability and higher accessibility of the substrate to the immobilized β-glucosidase. Conclusion: Response surface methodology (RSM) was proved to be much economical for optimum immobilization of β-glucosidase into chitosan beads.