An air-lift biofilm reactor for the production of γ-decalactones by Yarrowia lipolytica

Microbial biofilms: a comprehensive review of their properties, beneficial roles and applications

Biofilms are microbial communities nested in self-secreted extracellular polymeric substances that can provide microorganisms with strong tolerance and a favorable living environment. Deepening the understanding and research on positive effects of microbial biofilms is consequently necessary, since most researches focuses on how to control biofilms formation to reduce food safety issues. This paper highlights beneficial roles of biofilms including the formation mechanism, influencing factors, health benefits, strategies to improve its film-forming efficiency, as well as applications especially in fields of food industry, agriculture and husbandry, and environmental management. Beneficial biofilms can be affected by multiple factors such as strain characteristics, media composition, signal molecules, and carrier materials. The biofilm barrier composed of beneficial bacteria provides a more favorable microecological environment, keeping bacteria survival longer, and its derived metabolites are better conducive to health. However, in the practical application of biofilms, there are still significant challenges, especially in terms of film-forming efficiency, stability, and safety assessment. Continuous research is needed to discover innovative methods of utilizing biofilms for sustainable food development in the future, in order to fully unleash its potential and promote its application in the food industry.

Characterization of the metabolism of the yeast Yarrowia lipolytica growing as a biofilm

Yarrowia lipolytica is a well-characterized yeast with remarkable metabolic adaptability. It is capable of producing various products from different carbon sources and easily switching between planktonic and biofilm states. A biofilm represents a natural means of cell immobilization that could support continuous cultivation and production processes, such as perfusion cultivation. However, the metabolic activities of Y. lipolytica in biofilms have not yet been studied in detail. Therefore, this study aimed to compare the metabolic activities of Y. lipolytica in biofilm and planktonic states. Conventionally, a stirred tank bioreactor was used to cultivate Y. lipolytica in a planktonic state. On the other hand, a trickle bed bioreactor system was used for biofilm cultivation. The low pH at 3 was maintained to favor polyol production. The accumulation of citric acid was observed over time only in the biofilm state, which significantly differed from the planktonic state. Although the biofilm cultivation process has lower productivity, it has been observed that the production rate remains constant and the total product yield is comparable to the planktonic state when supplied with 42% oxygen-enriched air. This finding indicates that the biofilm state has the potential for continuous bioprocessing applications and is possibly a feasible option.

Biotransformation of ricinoleic acid to γ-decalactone using novel yeast strains and process optimization by applying Taguchi model

Flavour molecules are generated now-a-days through microbial fermentation on a commercial scale. γ-Decalactone (GDL) is an important molecule due to its long-lasting flavouring impact as buttery, coconut and peach-type. In the current study, 33 microorganisms were isolated from different fruit sources, and their screening for target GDL production was performed. Using DNA sequencing, two potential strains yielding good amounts of GDL were identified from pineapple and strawberry fruits. The identified strains were Metschnikowia vanudenii (OP954735) and Candida parapsilosis (OP954733), and further optimized by Taguchi method. The effectiveness of lactone production is influenced by the rate of microbial growth under various operating conditions. The factors such as substrate concentration, pH, temperature, cell density and rotation (rpm) with 3 levels were applied for the GDL production using M. vanudenii (OP954735) and C. parapsilosis (OP954733) strains. The results revealed that the highest molar conversion of GDL was 24.69% (115.7 mg/g quantitative yield) and 52.69% (272.0 mg/g quantitative yield) at the optimal conditions using SB-62 and PA-19 strains, respectively. The two novel strains are reported for the first time for production of γ-decalactone and overall, this study opens up the possibility of using Taguchi design for large scale up process development for producing food flavours utilising environmentally friendly natural strains.

Metabolic and Process Engineering for Producing the Peach-Like Aroma Compound γ-Decalactone in Yarrowia lipolytica

Due to its strong and unique peach-like aroma, γ-decalactone is widely used in dairy products and other foods or beverages. The oleaginous yeast Yarrowia lipolytica, which is generally regarded as safe, has shown great potential in the production of this flavor compound. Recently, the development of metabolic and process engineering has enabled the application of Y. lipolytica for the production of γ-decalactone. This Review summarizes the relevant biosynthesis and degradation pathways of Y. lipolytica, after which the related metabolic engineering strategies to increase the accumulation of γ-decalactone are summarized. In addition, the factors affecting γ-decalactone accumulation in Y. lipolytica are introduced, and corresponding process optimization strategies are discussed. Finally, the current research needs are analyzed to search for remaining challenges and future directions in this field.

Use of Pressurized and Airlift Bioreactors for Citric Acid Production by Yarrowia lipolytica from Crude Glycerol

Citric acid production is generally carried out in an aqueous medium in stirred tank reactors (STR), where the solubility of oxygen is low and the oxygen demand of microbial cultures is high. Thus, for this bioprocess, providing adequate oxygen mass transfer rate (OTR) from the gas phase into the aqueous culture medium is the main challenge of bioreactor selection and operation. In this study, citric acid production by Yarrowia lipolytica W29 from crude glycerol, in batch cultures, was performed in two non-conventional bioreactors normally associated with high mass transfer efficiency: a pressurized STR and an airlift bioreactor. Increased OTR was obtained by raising the total air pressure in the pressurized STR and by increasing the aeration rate in the airlift bioreactor. An improvement of 40% in maximum citric acid titer was obtained by raising the air pressure from 1 bar to 2 bar, whereas, in the airlift bioreactor, a 30% improvement was attained by increasing the aeration rate from 1 vvm to 1.5 vvm. Both bioreactor types can be successfully applied for the citric acid production process using alternative ways of improving OTR than increasing mechanical stirring power input, thus leading to important operating saving costs.

Production of lactones for flavoring and pharmacological purposes from unsaturated lipids: an industrial perspective

The enantiomeric pure and natural (+)-Lactones (C ≤ 14) with aromas obtained from fruits and milk are considered flavoring compounds. The flavoring value is related to the lactones' ring size and chain length, which blend in varying concentrations to produce different stone-fruit flavors. The nature-identical and enantiomeric pure (+)-lactones are only produced through whole-cell biotransformation of yeast. The industrially important γ-decalactone and δ-decalactone are produced by a four-step aerobic-oxidation of ricinoleic acid (RA) following the lactonization mechanism. Recently, metabolic engineering strategies have opened up new possibilities for increasing productivity. Another strategy for increasing yield is to immobilize the RA and remove lactones from the broth regularly. Besides flavor impact, γ-, δ-, ε-, ω-lactones of the carbon chain (C8-C12), the macro-lactones and their derivatives are vital in pharmaceuticals and healthcare. These analogues are isolated from natural sources or commercially produced via biotransformation and chemical synthesis processes for medicinal use or as active pharmaceutical ingredients. The various approaches to biotransformation have been discussed in this review to generate more prospects from a commercial point of view. Finally, this work will be regarded as a magical brick capable of containing both traditional and genetic engineering technology while contributing to a wide range of commercial applications.

Novel two-stage solid-state fermentation for erythritol production on okara-buckwheat husk medium

An economical model of two-stage solid state fermentation (SSF) (prefermentation stage with Mucor flavus and in situ erythritol fermentation stage with Yarrowia lipolytica) for enhancing erythritol production was investigated. Buckwheat husk (BH) was utilized as inert support for the first time and okara as the substrate. Morphological properties suggested yeast cells were exposed in adequate oxygen leading to high erythritol yield, and enzyme activities analysis indicated M. flavus and Y. lipolytica grew and cooperated well during the two ferment stages. Maximum erythritol production (143.3 mg/gds) was obtained from okara-BH mixture (5:2, w/w) supplemented with 0.01 g/gds NaCl, with an initial moisture content of 60% and pH of 4.0 for 192 h, while undesired mannitol and citric acid were suppressed. Compared with submerged fermentation, two-stage SSF was short period, energy conserving and operable for erythritol production from insoluble wastes, and this is the first report on erythritol production via SSF.

Aroma compounds production by solid state fermentation, importance of in situ gas-phase recovery systems

Flavour and fragrance compounds are extremely important for food, feed, cosmetic and pharmaceutical industries. In the last decades, due to the consumer's increased trend towards natural products, a great interest in natural aroma compounds has arisen to the detriment of chemically synthesised ones. Recently, solid state fermentation (SSF) has been applied in the production of many metabolites. Aroma compounds can be produced by SSF with a higher yield compared to submerged fermentation (SmF). In SSF processes, aroma compounds can be produced in the solid matrix or in the headspace, but they can be lost or stripped when aeration is required. This review focuses on the production of aroma compounds by SSF processes with a special highlight on in situ systems to recover the volatiles released in the gaseous phase and stripped due to aeration. Following a brief presentation of specificities of SSF processes concerning the choice of microorganisms and the solid matrix used for the production of aroma compounds, bioreactor aspects, factors affecting production of aroma compounds and in situ gas phase aroma recovery systems in aerated SSF bioreactors are discussed.

Biotechnological production of γ-decalactone, a peach like aroma, by Yarrowia lipolytica

The request for new flavourings increases every year. Consumer perception that everything natural is better is causing an increase demand for natural aroma additives. Biotechnology has become a way to get natural products. γ-Decalactone is a peach-like aroma widely used in dairy products, beverages and others food industries. In more recent years, more and more studies and industrial processes were endorsed to cost-effect this compound production. One of the best-known methods to produce γ-decalactone is from ricinoleic acid catalyzed by Yarrowia lipolytica, a generally regarded as safe status yeast. As yet, several factors affecting γ-decalactone production remain to be fully understood and optimized. In this review, we focus on the aromatic compound γ-decalactone and its production by Y. lipolytica. The metabolic pathway of lactone production and degradation are addressed. Critical analysis of novel strategies of bioprocess engineering, metabolic and genetic engineering and other strategies for the enhancement of the aroma productivity are presented.