research on vinegar production process and product development fruit vinegar made from pineapple

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURAL AND FORESTRY TRINH MANH TRUONG RESEARCH ON VINEGAR PRODUCTION PROCESS AND PRODUCT DEVELOPMENT FRUIT VINEGAR MADE FROM PINEAPPLE BACHELOR

THAI NGUYEN UNIVERSITY

UNIVERSITY OF AGRICULTURAL AND FORESTRY

TRINH MANH TRUONG

RESEARCH ON VINEGAR PRODUCTION PROCESS AND PRODUCT DEVELOPMENT FRUIT VINEGAR MADE FROM PINEAPPLE

BACHELOR THESIS

Study Mode: Full-time

Major: Food Technology

Faculty: International Programs Office Batch: 2017 - 2021

Superviso: Dr Pham Bang Phuong

Thai Nguyen – 2021

Abstract: The objective of this study is to improve the production of fruit vinegar made from pineapples purchased at Tuc Duyen wholesale market, Thai Nguyen city The submerged fermentation technique was used in this study The findings suggest that fermentation should comply with the pineapple vinegar fermentation process, with The optimal the amount of dry substance dissolving fermentation to be 6 oBx a pH of 5.5 being considered the ideal ratio, the 5% dilution of ethyl alcohol is applied In addition, temperature is an important factor that greatly affects the setting of a temperature 28oC in the appropriate temperature range for bacteria that can sustain life and produce a certain amount of acetic acid if the temperature is too high too low or too high the bacteria will stop growing Furthermore, a fermentation time of 20 days was observed and was limited in the process because it was found that too short a fermentation time was not enough for the bacteria to grow and carry out the metabolism if the fermentation time was too short If the fermentation time is prolonged, the bacteria will continue to metabolize, it will use the same amount of acetic acid that has been created to get energy for life activities to continue Research shows that the optimization done helps to offer more choices about flower vinegar for consumers

Keywords: Fruit vinegar, Pineapple, Fermentation methods, submerged fermentation, product diversification

Number of pages:

ACKNOWLEDGEMENT

Assigned by teachers of Faculty of Biotechnology & Food Technology, Thai Nguyen University of Agriculture and Forestry, after nearly 6 months of internship, I have completed this graduation thesis

In order to complete the assigned tasks, in addition to my own learning efforts, I also have the dedicated guidance of teachers, siblings and friends at the Faculty of Biotechnology & Food Technology

I sincerely thank my teacher – Dr Pham Bang Phuong, who did not hesitate to guide me, orient me, let me complete my task well

I would like to thank my teachers for helping, encouraging and creating favorable conditions for me in terms of facilities, equipment and tools during the course of the thesis The teachers of the Department of Biotechnology & Food Technology, Thai Nguyen University of Agriculture and Forestry dedicatedly taught and imparted knowledge to me throughout the course

However, due to limited professional knowledge and a lack of practical experience, the content of the report cannot avoid shortcomings officials and employees at the school and the facilities and businesses that I have practiced to make this report more complete

Once again, I would like to send my most sincere thanks to the teachers, friends and brothers and sisters at the Faculty of Biotechnology & Food Technology!

Thai Nguyen, October 20, 2021

TRường

Trinh Manh Truong

PART II: LITERATURE REVIEW 7

2.1 Scientific basis of the topic 7

2.1.1 Overview of pineapple ingredients 7

2.1.2 Nutritional composition and uses of pineapple 8

2.1.3 Research works in the world and in the country 9

2.2 Acetic Acid Strain 10

2.2.1 Characteristics of acetic bacteria 11

2.2.2 Classification of acetic bacteria 12

2.3 Overview of vinegar 14

2.5.1 Acidification of fermentation fluid 22

2.5.2 Ethyl alcohol content in vinegar fermentation solution 22

2.5.3 Substances C, N, P and trace elements 23

2.5.4 The causes of quality deterioration of vinegar fermentation: 23

2.5.5 Stages after harvesting vinegar 24

PART III: METHOD 25

3.1 Objects, materials, time and place of research: 25

3.4.3 Data processing methods 36

PART IV RESULT AND DISCUSSION 36

4.1 Research results 36

4.1.1 Research results to determine the amount of dry substance dissolving

fermentation pineapple 36

4.1.2 Research results to determine the suitable pH for fermentation 38

4.1.3.Research results determine the suitable fermentation temperature for fermentation 40

4.1.3 Research results determine the appropriate fermentation time for fermentation 42

4.1.4 Sensory evaluation results of the product 44

4.2 Data processing method 44

PART V CONCLUSION AND SUGGESTION 47

LIST OF FIGURE

Figure 2.1 Pineapple ropes, flowers and seeds 9Figure 2.2 Structure of acetic acid 11

Figure 2.3 Acetic bacteria in vinegar fermentation Error! Bookmark not defined

Figure 2.4 Studyto the experimental determine the pH of the fermentation process.Error! Bookmark not defined.

Experiment 3 Study to determine the fermentation temperature of acetic acid fermentation 29 Experiment 5 The sensory quality criteria of the product 30 Experiment 6 Building a process to produce fruit vinegar from pineapple 31

Figure 4.1 Graph showing the influence of sugar content suitable for fermentation:Error! Bookmark not defined.

Figure 4.2 The research results determine the suitable pH 38 Figure 4.2 Research results determine the suitable fermentation temperature for fermentation: 41 Figure 4.3 Research results determine the appropriate fermentation time for fermentation 42

LIST OF TABLE

Table 2.2: Nutritional table of ingredients in pineapple 8

Table 2.3: Analysis of boiling point of acetic acid Error! Bookmark not defined Table 3.1 Table of materials and equipment used in the study 25

Table 3.2 Table of research chemicals used in the research 25

Table 3.3: Table of experimental layout to determine the influence of sugar content suitable for fermentation 28

Table 3.4: Table of experimental layout to determine pH of fermentation 29

Table 3.5: Table of experimental layout to determine fermentation temperature 29

Table 3.5: Weight factor table 34

Table 3.6 Quality rating scale for products 35

Table 3.7 Scoring table describing in detail the sensory quality assessment of fruit vinegar products 35

Table 4.1: Research results to determine the influence of sugar content suitable for fermentation Error! Bookmark not defined Table 4.2 Research results determine the suitable pH 38

Table 4.2 Research results determine the suitable fermentation temperature for fermentation: 40

Table 4.3 Research results determine the appropriate fermentation time for fermentation: 42

PART I: INTRODUCTION 1.1 Question

In the northern mountainous provinces, pineapple has an important position in vegetable production because it can withstand external conditions and recovers capital early, so it is one of the strategies to improve farmers' lives Because of its potential, it is planted in many localities throughout the provinces of Bac Kan, Phu Tho, Nghe An, Lam Dong, Tien Giang,

Nowadays, the demand of consumers to use natural food products seems to become a trend and the research works on them are also constantly evolving and the effectiveness of different types of food This product is quite high compared to similar synthetic products Practical studies have shown that when using products of plant origin, there are few harmful side effects and this is an important reason that today natural products are increasingly developed strong

Vietnam has very favorable natural conditions for the development of fruits, in which there are many species of plants containing natural nutritional value that can take advantage of the flesh of the fruit In particular, pineapple tree is a potential plant, but has not been exploited and taken advantage of properly In recent years, the expansion of pineapple growing area has become rampant, with no clear market orientation, so people's consumption and purchase of pineapples has become precarious, depending entirely on traders Meanwhile, the area of raw materials for citrus crops such as pineapple forest in and outside the province has grown very strongly, consumers have more choices when buying fruit for food

The reasons make the market price of this fruit tree much lower, plus extreme weather, prolonged heavy rain at the time of harvest, which reduces yield due to rotting and damaged pineapples, which have caused pineapple gardens to fall From a place of high economic profit, it becomes a crop of low economic value and people have a need to destroy gardens and change crop structure, thus helping farmers to solve the urgency of the topic should be taken care of and implemented

The in practice, identified as a key agricultural product of some provinces, many topics and projects develop growing areas, research and apply technological processes in cultivation to increase productivity and quality for pineapple species has been implemented, there are many dried products, jams, canned pineapple juice from fruits like on the Vietnamese market We have an abundant source of domestic products, but we have not taken full advantage of it local people consume pineapple That situation it is necessary to research and find solutions to increase the value of pineapples by taking advantage of raw materials that are poorly designed pineapples, falling pineapples to avoid waste Realizing that pineapple contains a lot of nutritional components and to help farmers consume agricultural products to new consumption directions for this fruit, bringing higher economic efficiency to pineapple farmers Stemming from the above practice, we conducted research on pineapple vinegar production process to improve the economic value and quality of the product

1.2 Objectives of the study

Overall objectives:

Study on the influence of factors affecting the pineapple vinegar production proces

The research results of the topic will provide new scientific data on:

- The influence of ingredients on fermentation was determined in pineapple vinegar fermentation

- Evaluate some factors affecting the pineapple vinegar production process - Developed a production process for pineapple vinegar

1.4 Limitations

Students gain practical experience in scientific research, consolidate theoretical knowledge, apply in practice to perfect themselves in order to develop foundations, skills at work, and practice professional attitudes correct, refer to observational

assessment, study, read more books and internet to understand more about the research topic accumulated experience must practice more research skills

- Follow the arrangement instructions of the trainers as well as the assistant coaches in the implementation of the topic Follow the work plan, provide timely supplementary instructions to suit the conditions of knowledge exchange activities from teachers in order to accumulate experience, carefully review the contents of preparing for the report and ask for opinions about problems that arise during the internship

- The research results of the topic will partly contribute to the study of the fruit vinegar production process that brings value, health and economy to the community

PART II: LITERATURE REVIEW 2.1 Scientific basis of the topic

2.1.1 Overview of pineapple ingredients

Scientific name: Pineapple Ananas comosus L (Merrill) Belongs to the family: Bromeliaceae

Genus: Ananas

Foreign names: Mauritius (India), Red Malacca (Malaysia), Sugarloaf (Philippines) , Champaka (Thailand)…

Vietnamese name: Dứa, Khóm…

Pineapple has the scientific name Anamas comosus L/(Merill), belongs to the family

Bromeliaceae, genus Ananas Pineapple is a tropical fruit tree, pineapple species brings very high nutritional value and is considered an ideal fruit for all ages, especially all pineapple products can be used as food, fertilizer

Vietnamese pineapple stands out with 3 main classification varieties:

- Queen group (Queens): Pineapple belongs to this group of medium weight and size, convex eyes, carrying capacity, dark yellow flesh, characteristic sweet aroma This is a group of pineapples with the highest quality that are commonly grown in our country and are called pineapple flowers or pineapples

- Cayene group (Caine) This type has a large fruit mass, sometimes up to 3 kg, ivory yellow flesh, more water, less fragrant and less sweet than pineapple flowers This variety in many countries in the region it is grown a lot for processing because its large fruit is easy to mechanize and gives high economic efficiency Currently, Vietnam is developing this pineapple variety (Singh et al., 2004)

- Spanish group (Spain) This pineapple has a larger fruit size than flower pineapple, The flesh of the fruit is pale yellow to white, less fragrant, sour, more watery

2.1.2 Nutritional composition and uses of pineapple

Pineapple is considered a fruit with a rich flavor and a very clear scent that is not mixed with other fruits that are rich in nutrients from the fruit pulp (Wooster and Blank,1950) gave the following results after analyzing the Cayenne pineapple variety grown in Hawaii, including the following components:

Table 2.2 Nutritional facts of ingredients in pineapple

Nutritional ingredients Ratio

a Pineapple ropes and flowers b Pineapple seeds

Figure 2.1 Pineapple ropes, flowers and seeds 2.1.3 Research works in the world and in the country Several studies on pineapples in the world

According to statistics (Anon, 2002) collected from FAO (Food and Agriculture Organization) of the United States, world pineapple production from 1999 to 2001 was 13,527,149 million tons and is estimated to be stable for 3 years World production has tripled in the last 30 years (3,833,137 in 1961 to 13,738,735 in 2001) The leading production countries in 2001 includeThailand (2,300,000 tons), the Philippines (1,571,904 tons) China (1,284,000 tons) The US is the largest pineapple importer from 1998 to 2000 with an average of 552597 thousand USD per year in canned, fresh and concentrated pineapple forms (Rohrbach et al., 2003)

According to statistics, the production of Smooth Cayene pineapple variety accounts for 70% of the world production and is mostly in canned form (about 95%) in so there has been pressure on investors to improve the Cayenne variety to provide a better form (Salewski and Scott, 2000)

Several studies on pineapples in the Vietnam

In Vietnam, according to research conducted by the Research Institute of Fruits and Vegetables, Cayenne have been gathered in our country including: Provinces with a large area of Cayenne pineapple such as Ninh Binh (700 ha), Nghe An (695 ha), Ha Tinh (438 ha), (Tuan and Tien, 2002) The origin of Cayene varieties grown in our country is usually imported from abroad and through crossbreeding (Tran The Tuc and Vu Manh Hai, 2002) Vietnam pineapple is a key fruit in processing export products, but the output is still very small compared to other countries in the region Raw materials supplied to processing plants are in a state of insufficient supply and demand due to the establishment of many pineapple processing factories with high capacity and modern technology such as An Giang, Ho Chi Minh, Can Tho

2.2 Acetic Acid Strain

Definition: Acetic fermentation is essentially the incomplete oxidation of ethanol to acetic acid under the action of bacteria Fermentation is “Effervescence” which is a biological process in redox reactions occur in microbial cells, in the absence of any oxidizing agents part of the organic matter is broken down to a reducing agent, the rest is broken down to an oxidizing agent [2] According to Pasteur's definition, fermentation is essentially an anaerobic process that occurs for the living activities of microorganisms to obtain energy (Mehaia and Cheryan, 1991; Tan, 2003)

The chemical formula of acetic acid is CH3COOH There is an OH group bonded with a CO group forming a COOH group, this group of COOH makes the molecule

Figure 2.2: Structure image of acetic acid 2.2.1 Characteristics of acetic bacteria

Nowadays, more than 20 species of bacteria capable of fermenting are collectively known as acetic bacteria (B2-2, B3-2, CN, C2, L2, LH1, VL2, K4, BD11, B2-3, KG1, NH2, CB, ST2.2, SKU) These bacteria are easy to find in the air, soil, water, juices, wine with low concentration, sugar solution easy to contact with air, easy to be slightly turbid, on the surface forming a thin surface, film thin smooth white gray or yellow

Pasteur assumed that the vinegar fermentation was caused by a bacteria

belonging to the acetobacter or bacterium group Acetic bacteria not only oxidize

ethyl alcohol to acetic acid, alcohol to acid, but they cannot oxidize methyl alcohol and higher alcohols In an environment with enough ethyl alcohol (5 - 13%), the main

product is acetic acid At lower alcohol concentrations, Acetic bacteria completely

oxidize alcohol to CO2 and H2O (Lương Đức Phẩm,1998)

Acetic bacteria are bacilli, non-spore forming, rod-shaped, oval, size: 0.8 * (1.0 - 3.0) µm, single, filamentous, chain, some spiral , spherical, bulging rods, club-

shaped these bacteria have movable species by means of cilia, and species that cannot move The cells small they are Gram-, The cell old can change Grams The mostly catalase positive, oxidase free, often pigmented Some strains produce pink scum by Porphyrins [3]

Acetic bacteria belong to the aerobic group Their growth rate is very fast, from one cell after 12 hours can reproduce into 17 million cells.In the process of growth and development form acetic acid, low acid concentrations will stimulate their growth [5]

Acetic bacteria have the ability to assimilate different carbon sources such as:

Ethanol, glucose, fructose, saccarose, maltose, glycerin, lactose for the source of minerals and vitamins, it requires pantothenic acid and minerals (K, Ca, Fe, S, P ) to be assimilated

Acetic bacteria species grow in the temperature range from 20 - 35 OC At a temperature of 23-30 OC promotes them to reproduce quite quickly, resistant to highly acidic environments, some can grow at pH = 5.6 - 6.2, the optimal pH < 4.5 - 5.5, the characterized by their ability to change cell shape Under abnormal growth conditions, cells appear to be large and long filaments, swollen, or have strange shapes [7]

2.2.2 Classification of acetic bacteria

Currently, in the world more than 20 species of Acetic bacteria have been found in the world, collectively known as Acetobacter: A fairly large bacillus belonging to

the obligate aerobic type, the temperature range for their growth is from 20 - 40 OC

Acetic bacteria belong to two genera Acetobacter and Acetomonas (cilia at the

tip) Many types grown for a long time on the medium, easily give rise to special

morphological forms (cells are enlarged or elongated, can branch) the widely distributed in nature, especially on food, fruits and air with yeasts on plant substrates

Here are a few species of Acetic bacteria with many practical implications:

- Acetobacter acetic: Short rod-shaped, non-spore forming, often joined together

in long chains The cytoplasm was stained with iodine for yellow color This variety can grow at an alcohol concentration of 11% and accumulate in media up to 6% acetic acid, the optimum temperature for growth is 34 OC

- Acetobacter pteurianum: Short rod-shaped, dead cells stained with iodine for

blue color

- Acetobacter orleameuse: Small rod-shaped, slightly pointed at both ends,

develops into a thin, but firm film on the surface of the culture solution Iodine-stained dead cells give a yellow color This variety can grow in 10 - 12%V alcohol solution and produce 9.5% acetic acid

- Acetobacter xylium: The ability to form strong and sometimes quite thick

films, this variety accumulates 4.5% acetic acid species is sometimes used with yeast to produce low-alcohol beverages

- Acetobacter curvum: 35 - 37 OC Raising this limit temperature, the variety grows weak and produces poor acid In fact, acetic fermentation is usually kept at a temperature of 32 - 34 OC for Ace bacteria Curvum

- Acetobacter suboxydans: This bacterium is widely used in the vitamin industry

to produce ascorbic acid (vitamin C) Bacterial strains of suboxydans, acetic acid is accumulated and retained in the environment without further oxidation, Species with high oxidizing capacity that continue to convert acetic acid are classified 13% [8]

Figure 2.3 Acetic bacteria in vinegar fermentation 2.3 Overview of vinegar

Vinegar is produced from naturally fermented fruit, has the advantage that in addition to the main ingredient is acetic acid, there are other nutrients such as sugar, organic acids, amino acids, vitamins, inorganic salts , trace elements, etc are very good for consumers' health

Our country is a dense agricultural country with a humid tropical climate, so the source of fruits in our country is extremely rich such as: bananas, apples, mango, pineapples, The output of these fruit products remains unresolved contribute to the enrichment and diversification of vinegar products and also the consumption direction, the output for fruit products is the production of vinegar contains a lot of nutrients such as: fiber, antioxidants and phytonutrients in tangerine have a number of vitamins, amino acids

Present-day, the estimated potential market for fruit vinegar is quite limited because for-profit businesses often have no nutritional content, and may even be harmful to the health of users, so they produce vinegar From pineapple raw materials, this is an abundant and rich source of raw materials, solving the problem of output for

fruit products, nutrients, and delicious taste (Chen et al., 2010; Horiuchi, Kanno, & Kobayashi, 2000)

a)History of vinegar:

In 1864, chemist Louis Pasteur proved that vinegar is the result of natural fermentation, he figured out why wine becomes vinegar by the discovery of microorganisms that will turn wine into vinegar produced by fermentation of raw materials containing starch or sugar, or produced by preparation from refined acetic acid called vinegar fermentation

Vinegar is an acidic liquid, formed from the fermentation of ethyl alcohol (C2H5OH), or from raw materials containing sugar or starch The main ingredients of vinegar are water and acetic acid (CH3COOH), the acid concentration is from 2 to 5%, the pH is from 4 to 5 Fruit vinegar is a product fermented from fruit materials containing sugar, water and acetic acid, fruit vinegar also contains many other acids, rich in amino acids, vitamins, inorganic salts and trace elements

Vinegar is divided into two types: Distilled vinegar and Mixed vinegar

Distilled Vinegar: (also known as rice vinegar) is the result of fermentation from raw materials containing starch and sugar Nutritional ingredients include acetic acid,

sugar, organic acids, vitamins, inorganic salts, etc …

There are also several other types of vinegar:

- Wine vinegar: It is a product of the fermentation of a diluted pure alcohol solution of sour fermentation of grape wine juice, with the addition of inorganic salts and nutrients

- Rice Vinegar "Rice Vinegar": is the product of sour fermentation, the rice starch has been converted into sugar and then into alcohol

- Malt vinegar "Malt vinegar": It is the product of sour fermentation, the starch solution has been converted into molasses malt

Mixed vinegar: (chemical vinegar) is industrially produced by taking the refined acetic acid of the chemical component as the main raw material, adding dilute H2O to form it, without adding any other nutritional ingredients

c) Chemical composition of fruit vinegar:

Fruit vinegar has a rich amino acid composition: 18 kinds of amino acids in the human body cannot be synthesized in vinegar, 8 amino acids that plants provide,in addition there are more than 10 types of acids: lactic acid, ketone-based acid, citric acid In fruit vinegar, there are vitamins B1, B2, C There are also trace elements:: Na, K, Ca, Fe, Cu, Zn, P

d)Uses of vinegar

- Regulating and stabilizing the acidic and alkaline environment in the body: According to nutritionists, vinegar is a physiological alkaline food through the process it produces an alkaline reaction Because the body daily absorbs a large amount of highly acidic foods such as meat, fish, eggs, etc., drinking or adding a little vinegar to food can neutralize the acidic environment

- Vinegar has anti-aging ability, limiting delaying the aging of the body, inhibiting and lowering the ability to form oxidized fat

- Eliminate Na + ions, inhibit excess salt in the body, thereby stabilizing blood

- Prevention of obesity: vinegar contains ammonium acid, in addition, vinegar also promotes the open metabolism in the body into a expendable form of energy

e) Vinegar fermentation mechanism

Fermentation is the oxidation of alcohol to acetic acid, by acetic bacteria, under aerobic conditions

The general equation of fermentation is:

C2H5OH + O2 CH3COOH + H2O + 117kcal

The reaction occurs in the bacterial cell For the reaction to take place, C2H5OH and O2 must be absorbed into the cell At that time, the oxidizing enzymes present in the cell of bacteria participate in oxidizing alcohol to form CH3COOH, which will exit the cell and dissolve in the medium solution

Figure 2.2 Oxidation of alcohol to acetic acid

In bacterial cells, oxidation occurs in a very complex way This process occurs in two stages The stages are summarized as follows:

C2H5OH + O2 CH3CHO + H2O Acetaldehyd CH3CHO + H2O CH3CH(OH)2

Hydrate acetaldehyd CH3CH(OH)2 + O2 CH3COOH + H2O

General procedure: C2H5OH + O2 CH3COOH + H2O

In addition to the ability to oxidize alcohol to acetic acid, acetic bacteria also have the ability to participate in converting other alcohols into corresponding acids and other substances

- Metabolism of propyonic acid propyonic alcohol - Metabolism of glycerin dioxyacetone alcohol - Metabolism of sobic sorbose

- Glucose metabolism gluconic acid - Metabolism of lactic acid glucosenic acid

It should be noted that, during alcoholic fermentation, acetic bacteria will participate, the oxidation of acetic acid to CO2 and H2O to receive energy for its growth and development CH3COOH + 2O2 CO2 + H2O Therefore, after fermentation, it usually leaves an alcohol content of about 0.3-0.5% so that bacteria can use alcohol without using acetic acid as an energy source

2.4 Fermentation techniques

In Vietnam, fermentation is the process of creating products by a certain volume of biomass with microorganisms Applying the following methods to improve skills and development determine the effectiveness of a method of producing acetic acid is the interface between oxygen of air and substrate with four methods of producing acetic acid by fermentation :

a) Slow fermentation can refer to

This method is considered the traditional French fermentation method

The raw material of this method is grapes, the acetic acid bacteria used for the

production process is Acetobacter orleaneuse

Procedure: During the fermentation process, people usually put 1/5 of the acetic acid into the fermentation tank with a capacity of ½ barrel volume, continue to give the grape juice so that the entire volume reaches 2/3 of the volume of the fermentation tank The purpose of adding acetic acid is firstly to create conditions for fermenting bacteria to grow, on the other hand, to prevent other bacteria from growing, without being mixed with impurities, for fermentation at a temperature of 23-34OC After a while on the surface will form a scum containing a lot of acetic acid

Therefore, oxidation is slow and ends after a few weeks the testing remaining alcohol, the vinegar will be removed and a new nutrient solution will be added If left for a long time, the quality of vinegar is rapidly degraded because the oxidation of vinegar occurs continuously fermenting, write the vinegar that grows to form a microbial network on the open surface, when it is shaken it will sink to consume the substrate without creating acetic acid Gradually, on the open surface, new bacterial gills are formed and the fermentation process continues the obtained vinegar usually contains 5-6% acetic acid to keep for a long time, it must be pasteurized Because of the limitation of three open surfaces, this method also has advantages: long fermentation time, low concentration of acetic acid, low yield

b) Fast fermentation method

This method is practiced by the Germans on an industrial scale

This method creates a phase contact surface between the bed gas and microorganisms thanks to the addition of plate material in the device, so the

productivity is higher This method is manipulated by watering the fermenter is filled with binder material and carries new bacteria on the surface The air goes in the opposite direction from the bottom to make the fermenter rapidly metabolized by bacteria, so the fermenter is high enough, the operation is well controlled, only the fermenter is too low once to get a thick vinegar at the bottom of the device In case the final fermenter contains a low amount of acetic acid, re-fermentation is carried out by pumping them back from the top

c) Submerged fermentation method

In this method, the air escaping from the fermenter will form a magic in which the solid phase is bacteria, the solid phase is the wort in fermenters called acetators, the fermenters transfer changed

This method is applicable to anaerobic and aerobic microorganisms For anaerobic culture, the culture process does not require aeration, only stirring, and for aerobic microorganisms, it is necessary to continuously aerate the use of aqueous medium so that the surrounding surface is in contact with the liquid nutrients, they will grow vertically on the media column in microbiological technology to apply antibiotics, single-cell proteins, enzymes, amino acids, bread yeast production, etc pesticides, microbial products as fertilizers, etc…

The submerged fermentation method includes process characteristics and changes tracking based on microbial species and stages of fermentation so the choice of temperature is very important, but along with that is determining the time to maintain the process at a stable level, eliminating redundant time points as well as

clearly defining time to properly stop the fermentation process to ensure product recovery and maximum yield

Through the above methods, the application of submerged fermentation to the research topic of pineapple vinegar needs to be carried out in order to study the influence and optimize the new processes to bring about constructive results as well as community as providing more choices for consumers

d) Mixed fermentation method

This is a hybrid between the fast and the sinking methods This fermenter consists of two parts:

- The upper part like generator with filling buffer, works on the principle of fast fermentation

- The lower part (the part containing the fluid after passing through the binder) is fitted with an aerator to form an additional oxidation zone as an acetator in the submerged method

The oxygen supply through the aerator is stopped (when the power is turned off) there is still no effect on the bacteria because at that time the ventilation valves in the device are opened and air enters through natural ventilation, so the micro membrane bacteria on the mattress still do not die.This method overcomes the advantages and disadvantages of the two methods above

2.5 Techniques to pay attention to when producing vinegar:

Acetic bacteria usually digest very little nutrients, so nutrients need to be added to develop the ability to ferment at low levels.The propagation medium needs to be acidified to increase growth stimulation and inhibit other bacteria

2.5.1 Acidification of fermentation fluid

In vinegar production, a certain amount of vinegar is added to the initial substrate to acidify the medium in order to: prevent the growth of harmful microorganisms, and put a certain amount of cells in the fermentation solution

Initial acidity can range from 2-6% According to a study by Eapen and Rao in 1979, the highest yield was obtained at an initial acidity of 2% Recent works show that to get higher acid content, fermentation is carried out at an initial acid concentration of 2-6% (Abrini et al., 1992) However, high acid content will limit the growth of bacteria and reduce the ability to ferment According to Henry, the initial acid concentration of 8% inhibited the activity of bacteria greatly The initial amount of acid required for activation is 2-2.5 (Nodes.E, 1986 ), 2% (Ebner, 1985)

2.5.2 Ethyl alcohol content in vinegar fermentation solution

Ethyl alcohol, like acetic acid, is an antiseptic against Acetobacter bacteria, it is used as a substrate Alcohol content can vary from 2 to 10% by volume, higher alcohol content will reduce fermentation yield Ebner (1985) and Heirich (1987) for ethyl alcohol use from 2 to 10% by volume The amount of ethyl alcohol maintained in the medium is always kept at 3-3.5% by volume (Nodes, 1986)

To avoid further oxidation to CO2 and H2O, an alcohol content of 0.2-0.5% by volume is required The amount of alcohol in vinegar inhibits the synthesis of oxidizing enzyme acetic acid and acetic salt (Dires, 1973)

In the study, no research was conducted on the percentage of alcohol affecting the pineapple vinegar fermentation, the determination by diluting the alcohol ratio with