Efficient Utilization of Fruit Peels for the Bioproduction of D-Allulose and D-Mannitol

Construction of a Plasmid-Free Escherichia coli Strain with Enhanced Heme Supply to Produce Active Hemoglobins

BACKGROUND

Heme is an important cofactor and plays crucial roles in the correct folding of hemoproteins. The synthesis of heme can be enhanced by the plasmid-based expression of heme biosynthetic genes. However, plasmid-based expression is genetically unstable and requires the utilization of antibiotics to maintain high copy numbers of plasmids.

METHODS

The rate-limiting steps in heme biosynthesis were first analyzed based on previous studies and the accumulation of heme intermediates was achieved by adding heme precursor (5-aminolevulinic acid, ALA). Next, the intracellular accumulation of porphyrin was increased by deleting the porphyrin transporter TolC. Finally, the heme synthetic genes were modified by integrating the hemA and hemL genes into the cheW and yciQ locus, assembling the rate-limiting enzymes HemC and HemD with RIAD-RIDD tags, replacing the promoters of hemE/hemH genes with the constitutive promoter PJ23100, and deleting the heme degradation gene yfeX.

RESULTS

An enhanced heme supply HEME2 strain was obtained with a heme titer of 0.14 mg/L, which was 4.60-fold higher than that of the C41(DE3) strain. The HEME2 strain was applied to produce human hemoglobin and leghemoglobin. The titer and peroxidase activity of human hemoglobin were 1.29-fold and 42.4% higher in the HEME2-hHb strain than the values in the control strain C41-hHb. In addition, the peroxidase activity and heme content of leghemoglobin were increased by 39.2% and 53.4% in the HEME2-sHb strain compared to the values in the control strain C41-sHb.

CONCLUSIONS

A plasmid-free Escherichia coli C41(DE3) strain capable of efficient and stable heme supply was constructed and can be used for the production of high-active hemoglobins.

Advances in the bioproduction of d-allulose: A comprehensive review of current status and future prospects

As living standards rise, the overconsumption of sugary and calorific foods has led to a rise in obesity, diabetes, and other diseases. In response to the increasing demand for healthier diets, the food industry is actively seeking sugar alternatives. Among these alternatives, d-allulose as a functional sweetener has garnered significant attention for its low-calorie content, low glycemic index, and health benefits. This review summarizes recent advancements in d-allulose research, including its physiological functions, potential applications, and bioproduction methods. This review consolidates the known physiological functions of d-allulose and assesses its potential applications in the food and medical industries. Furthermore, the review explores recent progress in biotechnological production technologies, such as enzymatic conversion and microbial fermentation, which are key to producing d-allulose. d-Allulose is a standout natural sweetener with low calories and a low glycemic index, providing health benefits like lowering blood sugar and lipids, antioxidants, preventing obesity, and regulating metabolism. In the food industry, d-allulose is suitable for use in a variety of products, including baked goods, beverages, confectionery, and yogurt. The primary methods for its production are enzymatic conversion and microbial fermentation, both of which offer scalable and sustainable approaches. Recent research has advanced the production of d-allulose using low-cost raw materials, including agricultural and forestry waste, and even CO2, highlighting a move towards more sustainable production methods. With its diverse physiological functions and broad application prospects, d-allulose holds significant potential for growth in both the food and healthcare sectors.

Application of Emerging Techniques in Reduction of the Sugar Content of Fruit Juice: Current Challenges and Future Perspectives

In light of the growing interest in products with reduced sugar content, there is a need to consider reducing the natural sugar concentration in juices while preserving the initial concentration of nutritional compounds. This paper reviewed the current state of knowledge related to mixing juices, membrane processes, and enzymatic processes in producing fruit juices with reduced concentrations of sugars. The limitations and challenges of these methods are also reviewed, including the losses of nutritional ingredients in membrane processes and the emergence of side products in enzymatic processes. As the existing methods have limitations, the review also identifies areas that require further improvements and technological innovations.

Low-calorie bulk sweeteners: Recent advances in physical benefits, applications, and bioproduction

At present, with the continuous improvement of living standards, people are paying increasing attention to dietary nutrition and health. Low sugar and low energy consumption have become important dietary trends. In terms of sugar control, more and more countries have implemented sugar taxes in recent years. Hence, as the substitute for sugar, low-calorie sweeteners have been widely used in beverage, bakery, and confectionary industries. In general, low-calorie sweeteners consist of high-intensity and low-calorie bulk sweeteners (some rare sugars and sugar alcohols). In this review, recent advances and challenges in low-calorie bulk sweeteners are explored. Bioproduction of low-calorie bulk sweeteners has become the focus of many researches, because it has the potential to replace the current industrial scale production through chemical synthesis. A comprehensive summary of the physicochemical properties, physiological functions, applications, bioproduction, and regulation of typical low-calorie bulk sweeteners, such as D-allulose, D-tagatose, D-mannitol, sorbitol, and erythritol, is provided.