Study of pineapple peelings processing into vinegar by biotechnology

Recent advances of fermented fruits: A review on strains, fermentation strategies, and functional activities

Fruits are recognized as healthy foods with abundant nutritional content. However, due to their high content of sugar and water, they are easily contaminated by microorganisms leading to spoilage. Probiotic fermentation is an effective method to prevent fruit spoilage. In addition, during fermentation, the probiotics can react with the nutrients in fruits to produce new derived compounds, giving the fruit specific flavor, enhanced color, active ingredients, and nutritional values. Noteworthy, the choice of fermentation strains and strategies has a significant impact on the quality of fermented fruits. Thus, this review provides comprehensive information on the fermentation strains (especially yeast, lactic acid bacteria, and acetic acid bacteria), fermentation strategies (natural or inoculation fermentation, mono- or mixed-strain inoculation fermentation, and liquid- or solid-state fermentation), and the effect of fermentation on the shelf life, flavor, color, functional components, and physiological activities of fruits. This review will provide a theoretical guidance for the production of fermented fruits.

Comparison of the Chemical Properties of Vinegar Obtained via One-Step Fermentation and Sequential Fermentation from Dragon Fruit and Pineapple

Dragon fruit has many potential health benefits. It is inexpensive and widely cultivated in Thailand. The addition of dragon fruit to pineapple vinegar may help enhance the total phenolic compounds and antioxidant activity. This study aimed to study and compare the chemical characteristics of vinegar produced via one-step fermentation of a mixture of pineapple and dragon fruit juice from Krok Phra District of Thailand using Saccharomyces cerevisiae var. burgundy with that obtained using sequential fermentation using Saccharomyces cerevisiae var. burgundy and Acetobacter aceti. When the two fermentation methods were compared on day 20, the maximum acetic acid concentration obtained from sequential fermentation was 5.79 ± 0.25%, which was higher than that obtained in one-step fermentation (1.93%). The total phenolic compound content in the mixed fruit vinegar obtained from sequential fermentation and one-step fermentation was 228.01 and 242.2 mg/L gallic acid equivalents, respectively. The antioxidant content of the products obtained in sequential and one-step fermentations was 187.91 mg/L GAE and 209.33 µg/g of Trolox equivalents, respectively, which was consistent with the total phenolic compound content. This indicated that the acetic acid content in the mixed pineapple and dragon fruit juice vinegar obtained using sequential fermentation was higher than that obtained using one-step fermentation although its total phenolic content and the antioxidant activities were slightly lower. These observations will be useful for improving vinegar fermentation in the area.

Comparison of the Chemical Properties of Pineapple Vinegar and Mixed Pineapple and Dragon Fruit Vinegar

Pineapples are a tropical fruit with high nutritional value and high vitamin and sugar contents. In this study, low-grade pineapples were fermented to produce vinegar using surface culture fermentation (SCF), which involved the addition of dragon fruit juice, to compare the quality and antioxidant activity of different preparations of vinegar. The highest acetic acid concentration (7.35%) was obtained from pineapple vinegar after 20 days of incubation. Vinegar made from mixed pineapple and dragon fruit juice without peel and vinegar with pineapple and dragon fruit juice with peel had acetic acid concentrations of up to 6.20% and 4.50%, respectively. The mixed-fruit vinegar of pineapple and dragon fruit juice with peel displayed the highest antioxidant activity at 210.74 µg/g TE, while no significant difference was found between the other two vinegars (189.52 vs. 187.91 µg/L TE). Notably, the volatile compounds detected in the vinegars were alcohols and esters, which may contribute to the distinct aroma. Overall, the addition of dragon fruit juice with peel to pineapple vinegar increased the phenolic content and antioxidant activity; however, fermentation was slightly slower than that of the other two test materials.

Vinegar: A functional ingredient for human health

Vinegar is a well-known natural food product derived from alcoholic and subsequently acetous fermentation of carbohydrate-rich foods. Vinegar is widely used in the food industry; domestically for pickling vegetables and fruits, and as an ingredient in condiments like salad dressings, ketchups, and mayonnaise; and traditionally as a food seasoning and preservative. Historically, vinegar has been used for medicinal purposes such as a cure for stomach aches, wounds, burns, rashes, and oedema conditions. Different types of vinegar are found worldwide such as rice, black, balsamic, grain, and fruit vinegars. These are produced from different raw materials, and using different fermentation methods to give unique tastes and flavours. Vinegar, while enhancing physiological functions such as lipid metabolism, blood glucose level control, and body weight management, also possesses anticancer, antibacterial, antioxidant, and anti-infection properties. It is considered as a good source material for many bioactive compounds including organic acids, melanoidins, polyphenols, ligustrazine, and tryptophol. The pharmacological and metabolic benefits of vinegar are believed to be due to these bioactive compounds present in vinegar. Acetic acid (CH3COOH) is the essential component of vinegar; it is slightly volatile and has a strong and sour aroma and flavour. Regular consumption of vinegar-containing foods is considered important for keeping many life-style related diseases like diabetes, hypertension, hyperlipidaemia, cancers, and obesity in check. Therefore, the present review aims at highlighting the health benefits associated with vinegar consumption for the physiological well-being of an individual.

Acetic acid bioproduction: The technological innovation change

Acetic acid is an organic acid of great importance globally and the demand of this product is currently increasing. The production of this acid has consequently aroused more and more interest over the years, especially for more sustainable processes. From a biological point of view, acetic acid can be produced by acetogenesis using inorganic substrates like CO₂ or CO (with acetogenic bacteria) and aerobic fermentation (with acetic acid bacteria or fungi). With the aim of investigating the progress of technological innovation, the methodology applied by this review was an analysis of the international patents with the Espacenet platform, which ensured a worldwide invention overview. Another criterion was the selection of a precise period of time, from 1990 to 2020. A patent review is able to create an overview of the inventions designed for the real scale implementation, providing a whole picture of the state of the art of the technological innovation change. In addition, the most representative works of literature, that consider the influence of operating conditions (T, pH, oxygenation), have been analysed for each process. The present review, with an innovative approach focused on the technological innovation change, highlighted the ongoing interest for acetic acid bioproduction by acetogenic and acetic acid bacteria. The number of patents related to acetic acid bacteria was consistent also in the past years, but recently the interest is moving forward the utilization of genetic engineering (36% of the patents) and new substrates, like agriculture waste (26% of the patens), responding to circular economy principles. On the other hand, the acetic acid production by acetogenic bacteria is most recent, with over the 90% of the patents developed in the last 10 years. In this case the interest is mainly focused on the use of synthesis gas as substrate, that could increase the process sustainability.

Biotechnological Processes in Fruit Vinegar Production

The production of fruit vinegars as a way of making use of fruit by-products is an option widely used by the food industry, since surplus or second quality fruit can be used without compromising the quality of the final product. The acetic nature of vinegars and its subsequent impact on the organoleptic properties of the final product allows almost any type of fruit to be used for its elaboration. A growing number of scientific research studies are being carried out on this matrix, and they are revealing the importance of controlling the processes involved in vinegar elaboration. Thus, in this review, we will deal with the incidence of technological and biotechnological processes on the elaboration of fruit vinegars other than grapes. The preparation and production of the juice for the elaboration of the vinegar by means of different procedures is an essential step for the final quality of the product, among which crushing or pressing are the most employed. The different conditions and processing methods of both alcoholic and acetic fermentation also affect significantly the final characteristics of the vinegar produced. For the alcoholic fermentation, the choice between spontaneous or inoculated procedure, together with the microorganisms present in the process, have special relevance. For the acetic fermentation, the type of acetification system employed (surface or submerged) is one of the most influential factors for the final physicochemical properties of fruit vinegars. Some promising research lines regarding fruit vinegar production are the use of commercial initiators to start the acetic fermentation, the use of thermotolerant bacteria that would allow acetic fermentation to be carried out at higher temperatures, or the use of innovative technologies such as high hydrostatic pressure, ultrasound, microwaves, pulsed electric fields, and so on, to obtain high-quality fruit vinegars.

Simultaneous vinegar fermentation from a pineapple by-product using the co-inoculation of yeast and thermotolerant acetic acid bacteria and their physiochemical properties

In the present study, a potential newly isolated thermotolerant acetic acid bacteria (TH-AAB), Acetobacter pasteurianus FPB2-3, with ethanol and acetic acid-tolerant properties was found to be very effective in the production of vinegar from pineapple peels as an alternative, inexpensive raw material using simultaneous vinegar fermentation (SVF). The results showed that using whole pineapple peel with the addition of diammonium phosphate (DAP) and MgSO₄ at an initial pH of 5.5 gave a slightly higher acetic acid content than that produced from the squeezed juice. Subsequently, the effects of sugar concentration and inoculation time of A. pasteurianus FPB2-3 on acetic acid production were examined. The results revealed that an increase in sucrose concentration led to the high production of ethanol, which resulted in the suppression of acetic acid production. Allowing for the inoculated yeast to ferment prior to inoculation of the AAB for 1 or 2 days resulted in a longer lag time for ethanol oxidation. However, acetic acid accumulation commenced after 5 days and gradually increased to the maximum concentration of 7.2% (w/v) within 16 days. Furthermore, scaled-up fermentation in 6 l vessels resulted in slower acetic acid accumulation but still achieved a maximum acetic acid concentration of up to 6.5% (w/v) after 25 days. Furthermore, the antioxidant capacity of the vinegar produced from pineapple peels (PPV) was slightly higher than that produced from the squeezed juice (PJV), which was consistent with the higher total phenolic compound content found in the PPV sample. In addition to acetic acid, a main volatile acid present in vinegars, other volatile compounds, such as alcohols (isobutyl alcohol, isoamyl alcohol, and 2-phenyl ethanol), acids (3-methyl-butanoic acid), and esters (ethyl acetate, 3-methyl butanol acetate, and 2-phenylethyl acetate), were also detected and might have contributed to the observed differences in the odour and aroma of the pineapple vinegars.

Role of social wasps in Saccharomyces cerevisiae ecology and evolution

Saccharomyces cerevisiae is one of the most important model organisms and has been a valuable asset to human civilization. However, despite its extensive use in the last 9,000 y, the existence of a seasonal cycle outside human-made environments has not yet been described. We demonstrate the role of social wasps as vector and natural reservoir of S. cerevisiae during all seasons. We provide experimental evidence that queens of social wasps overwintering as adults (Vespa crabro and Polistes spp.) can harbor yeast cells from autumn to spring and transmit them to their progeny. This result is mirrored by field surveys of the genetic variability of natural strains of yeast. Microsatellites and sequences of a selected set of loci able to recapitulate the yeast strain's evolutionary history were used to compare 17 environmental wasp isolates with a collection of strains from grapes from the same region and more than 230 strains representing worldwide yeast variation. The wasp isolates fall into subclusters representing the overall ecological and industrial yeast diversity of their geographic origin. Our findings indicate that wasps are a key environmental niche for the evolution of natural S. cerevisiae populations, the dispersion of yeast cells in the environment, and the maintenance of their diversity. The close relatedness of several wasp isolates with grape and wine isolates reflects the crucial role of human activities on yeast population structure, through clonal expansion and selection of specific strains during the biotransformation of fermented foods, followed by dispersal mediated by insects and other animals.