Proposals for the residues recovery: Orange waste as raw material for new products

Plant biomass is an abundant renewable resource on Earth. Microorganisms harvest energy from plant material by means of complex enzymatic systems that efficiently degrade natural polymers. Intriguingly, microorganisms have evolved to exploit these ancient mechanisms to also decompose synthetic plastic polymers. In this Review, we summarize the mechanisms by which they decompose non-starch plant biomass and the six major types of synthetic plastics. We focus on the structural features of the enzymes that contribute to substrate recognition and then describe the catalytic mechanisms of polymer metabolism. An understanding of these natural biocatalysts is valuable if we are to exploit their potential for the degradation of synthetic polymers. Microorganisms enzymatically degrade natural polymers and synthetic plastics to enable a sustainable environment. This Review describes common features of these enzymes and how they can be harnessed to convert waste into useful precursors.

Enzymatic degradation of plant biomass and synthetic polymers

Recent advances in the sustainable design and applications of biodegradable polymers.

Bioprocessing of citrus waste peel for induced pectinase production by Aspergillus niger; its purification and characterization

Neutrase, a commercial preparation of Bacillus subtilis, was covalently immobilized on alginate−glutaraldehyde beads. Immobilization conditions and characterization of the immobilized enzyme were investigated. Central composite design and response surface methods were employed to evaluate the effects of immobilization parameters, such as glutaraldehyde concentration, enzyme loading, immobilization pH, and immobilization time. Under optimized working conditions (2% alginate, 6.2% glutaraldehyde, 61.84 U mL−1 Neutrase, pH 6.2, and 60 min) the immobilization yield was about 50%. The immobilized enzyme exhibited higher Km compared to the soluble enzyme. The pH−activity profile was widened upon immobilization. The optimum temperature was shifted from 50 to 60 °C, and the apparent activation energy was decreased from 47.7 to 22.0 kJ mol−1 by immobilization. The immobilized enzyme also showed significantly enhanced thermal stability.

Neutrase Immobilization on Alginate−Glutaraldehyde Beads by Covalent Attachment

A plethora of solid substrates, cultivation conditions and enzyme assay methods have been used for efficient production and estimation of polygalacturonase and pectin methylesterase enzymes. Recent developments in industrial biotechnology offer several opportunities for the utilization of low cost agro-industrial waste in Solid State Fermentation (SSF) for the pectinolytic enzyme production using fungi. Fruit waste mainly citrus fruit waste alone and along with other agro-industrial waste has been explored in SSF for enzyme production. Agro-industrial waste, due to the economic advantage of low procuring cost has been employed in SSF bioreactors for pectinolytic enzyme production. Acidic pectinases produced by fungi are utilized especially in food industries for clarification of fruit juices. This review focuses on the recent developments in SSF processes utilizing agro-industrial residues for polygalacturonase and pectin methylesterase production, their various assay methods and applications in fruit juice industries.

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Pectinolytic enzymes-solid state fermentation, assay methods and applications in fruit juice industries: a review

Production of polygalacturonase by immobilized cells of Aspergillus niger using orange peel as inducer

Beverage industry for its fruit juice products and fruit softening has been using cell wall degrading enzymes such as pectinases, cellulases, and proteases. The pectin in the middle lamella of plant tissues is enzymatically degraded by protopectinase, pectin methylesterase, pectin lyase, and polygalacturonase to completely hydrolyze the galacturonan polymer to its constituent galacturonic acid. This improves the yield and clarification of various fruit juices. The acidic pectinases are used extensively in fruit juice manufacturing individually or synergistically with cellulases and proteases. Various microbial—fungal and bacterial—sources have been employed for production of pectinases using solid state as well as submerged fermentation. The purified or partially purified polygalacturonase and pectin methylesterase have been employed for clarification of various fruit juices in solutions or by using bioreactors. Pectinases are an important biochemical tool for fruit liquefaction, pressing, clarification, and production of clear concentrated fruit juices. This chapter contemplates the pectin structure, the hydrolyzing enzymes, their sources, production, and their application in the beverage industry.

Pectinases: Production and Applications for Fruit Juice Beverages

Production of an extracellular, acidic pectin methylesterase was carried out by a newly isolated fungal strain identified as Aspergillus tubingensis using dried papaya peel under solid state fermentation. Response Surface Methodology involving Box-Behnken Design was employed for the optimization of process parameters viz. moisture content, period of fermentation, inoculum size and particle size of papaya peels. Maximum yield of pectin methylesterase was 246.83 U/g dried substrate, obtained by inoculating 10 g of papaya peel with 1×10 7 spores/ml, at initial 86% moisture content and particle size 2 mm after 120 h of fermentation period. The nearly same optimized values (R 2 =0.99) and experimental values (R 2 =0.96) indicated the validity of the statistical model. Under these experimental designs, the yield of pectin methylesterase increased 3.39 fold, which was much efficient and economical than “one factor at a time” methodology. Crude pectin methylesterase showed maximum activity at 50 °C and pH 4.6. Addition of partially purified enzyme increased the pineapple juice clarity as indicated by an increase in % transmission at 650 nm from 3.1 to 19.5 and decrease in pH from 4.3 to 3.0.

Papaya peel valorization for production of acidic pectin methylesterase by Aspergillus tubingensis and its application for fruit juice clarification

Proteolytic enzymes hold a pivotal position in numerous industrial processes where hydrolysis of protein molecules is required under precise conditions. The emerging trend of biotechnological applications in recent years has witnessed a renewed interest in alkaline serine proteases extending their utility in detergent, leather, textile, food and pharmaceutical industries. A variety of microorganisms have been reported to produce alkaline serine proteases on a large scale, however, extensive research to find an alkaline serine protease with desirable characteristics such as significant catalytic efficiency, expanded stability and broad substrate specificity is still ongoing. Although submerged fermentation dominates the commercial enzyme production, recent reports have emphasized on solid state fermentation technology which can reduce major cost associated with the enzyme production. In the present review, recent research on alkaline serine proteases along with their novel properties and production using solid state fermentation have been discussed.

Sadhana Nighojkar

Papers

Pectinolytic enzymes-solid state fermentation, assay methods and applications in fruit juice industries: a review

Production of polygalacturonase by immobilized cells of Aspergillus niger using orange peel as inducer

Pectinases: Production and Applications for Fruit Juice Beverages

Papaya peel valorization for production of acidic pectin methylesterase by Aspergillus tubingensis and its application for fruit juice clarification

Microbial alkaline serine proteases: Production, properties and applications