Weak acids’ microbial and sensorial effect on marinated herring

Abstract

Marinated herring is a food product usually with a sauce containing acetic acid. In this project the weak acids malic acid, citric acid, and lactic acid were evaluated for use in the sauce for marinated herring instead of using acetic acid. The microbial and sensorial effects of the acids were evaluated.

From the sensorial test, the marinated herring in a sauce with lactic acid was chosen as the favourite of the majority in the sensory panel since it was milder than the rest. The type with sauce containing malic acid was the least favoured due to high sourness and unbalanced flavours. It was concluded from the sensorial test that there were only small differences between the versions. The texture of the herrings was believed by the panel to differ between the acids but texture analysis showed no significant difference.

Accelerated test and microbial tests with the pickled herring jars to evaluate the shelf life indicated that there was no big difference in the presence of microorganisms depending on the acid. In the project accelerated tests using MRS growth medium inoculated with Lactobacillus plantarum (L. plantarum) CCUG 30503 T were performed. The MRS was modified with sodium chloride and weak acids to resemble the environment in a pickled herring jar. The results indicated that L. plantarum can grow well in the presence of acetic acid, malic acid, citric acid, and lactic acid. Malic acid and citric acid had least effect on the bacteria while the acetic acid had the highest effect resulting in a lower growth. In the samples with lactic acid the level of L. plantarum was stable on a higher concentration than in the rest of the samples when the highest concentration had been reached.

Popular Abstract

A sour history about pickled herring and microorganisms

To use another weak acid than acetic acid in the traditional pickled herring and maintain satisfactory preservation against spoiling microorganisms and get a new sensorial experience, is that possible?

Pickled herring is a product that has been eaten in Sweden for the last 250 years and it plays a big role in the Swedish cuisine. The fish product with its salty, sweet and sour flavours is eaten by many Swedes at celebrations like Easter, Midsummer and Christmas. Basically, it is raw herring that is put into a sauce containing salt, sugar, flavourings and a weak acid which normally is acetic acid. To get new flavours and a new product the weak acid can be changed into another weak acid like lactic acid, citric acid or malic acid. Acetic acid gives the product a rather sharp sour taste while lactic acid with its mild flavour, citric acid with a fresh flavour, and malic acid with the fruity flavour would give a new experience of the herring. In this project pickled herring with the different weak acids were produced according to a modified existing recipe and a panel evaluated the sensorial effects of the acids. The surprising result was that it was not the common type with acetic acid that was the favourite but rather the type with lactic acid due to the milder sourness. The type with acetic acid received the second place.

Microorganisms in pickled herring are bad since they can spoil the product or even worse, make it harmful to eat. In pickled herring lactic acid bacteria can be a spoiling organism and the big enemies of all unwanted microorganisms in product are the low pH and the rather high salt concentration. The acid gives the low pH and if the acid molecules can pass through the cell wall of the microorganism the organism will have a hard time and slowly die out. Depending on the properties of the acid and the pH of the surroundings (the herring) the acids have different effect on microorganisms. To change the acid in pickled herring is a bit tricky. Some acids are more microbially effective at higher pH and some at lower pH and at the same time the pH has to be lower than 4.5 to exclude the risk of very dangerous organisms. At the normal pH 4.2 of pickled herring the acetic acid is supposed to be the most effective but can the other mentioned acid be as effective and also give the herring a new sensorial experience?

Several microbial tests were therefore performed with herring in sauce with lactic acid, malic acid, citric acid and acetic acid. All of the tests indicate that all acids work fine against spoilage during the test period. In the experiments some herring jars were incubated in room temperature to speed up the growth of eventual microorganisms. Some jars were stored up to 14 weeks in the normal storage temperature in a refrigerator.

To deeper evaluate the effect of the acids against spoiling microorganisms the lactic acid bacterium Lactobacillus plantarum were inoculated in a nutrient medium (MRS). The MRS was modified to resemble the environment in a pickled herring jar with a higher salt concentration and pH of 4.2 or 5.0 with the four mentioned acids. The samples were incubated in room temperature for two weeks and the concentrations of the L. plantarum were measured regularly. It can be concluded that L. plantarum was growing perfectly fine and it does not bother the high salt concentration or the low pH. There were differences in growth between the acids in especially the samples with the lower initial pH where the growth of the bacteria was slower in acetic acid and lactic acid MRS.

The results from the microbial experiments with the herring jars and modified MRS can be used for further studies to determine the shelf life of the herring using different weak acids. Who knows, next year we might see pickled herring with the taste of lactic acid in the stores.

• author: Larsson, Jennika
• supervisor: Jenny Schelin
• organization: Applied Microbiology; Biotechnology
• course: KMB820 20161
• year: 2016
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering; Agriculture and Food Sciences
• keywords: sensorial test, Lactobacillus plantarum, acetic acid, malic acid, citric acid, Marinated herring, lactic acid, applied microbiology, teknisk mikrobiologi, MRS, accelerated test
• language: English
• id: 8892714
• date added to LUP: 2016-10-07 15:06:23
• date last changed: 2016-10-07 15:06:23