Pickling dates back to 2000 BC to Mesopotamia, where cucumbers from India were pickled in the Tigris Valley. Pickling is a means of preserving food in a brine solution, typically comprised of vinegar, salt, seasonings. These acidic, salty liquids are resistant to microbial growth, which preserves the flavour and quality of fresh foods immersed in brine. Many foods are pickled: from vegetables, such as cucumbers, peppers, and radishes; to animal products like eggs and even pig’s feet.
The lacto-fermentation method is a common type of pickling. In this method, vegetables are placed in saltwater brine. Then, lactic acid fermentation microorganisms are introduced or develop naturally. These organisms convert some of the sugars in the vegetables into lactic acid. The lactic acid production increases the acidity of the brine solution and lowers the pH. Once complete, the pH of the brine will be less than 4.6. It is important for the pH to be below 4.6 because microbial growth is greatly inhibited below a pH of 4.6, which ensures that the pickled product is shelf stable and not prone to microbial spoilage. Alternatively, an acidified brine of vinegar and salt can achieve similar results to lacto-fermented pickles.
When producing pickles on a large scale, the pickling brine solution must be prepared consistently in order to ensure a quality product. Salinity, acidity, and pH of the brine will affect the taste and consistency of the final products. For lacto-fermented pickles, if the salinity of the brine is too low, other non-desirable microorganisms may colonise the brine and cause the pickles to spoil. If the salinity is too high, lactic acid bacteria will not be able to thrive.
A pickling company contacted Hanna Instruments about automating their titrations for salt and acidity for their pickled food products. The customer asked about a means of increasing sample throughput, improving accuracy and repeatability, and improving measurement reporting and traceability. The customer is a large-scale food processor whose product offerings vary based on their contracts. The company prepares brines ranging in salinity from 3.5% to 10% NaCl and acidity from 0.8 to 6.0% acetic acid. Based on their quality control testing guidelines, each batch of brine has to be tested in triplicate for both salt and acidity to ensure that the product meets internal quality standards. This meant that on busy days, the quality lab was processing as many as 10 batches per hour, requiring 60 manual titrations per hour to meet QC guidelines.
Hanna Instruments offered the HI902C Automatic Potentiometric Titration System and HI921 Autosampler. The customer appreciated that the HI902C supported two analogue boards, allowing them connect both a pH electrode for acidity titrations and silver sulphide ISE for salt titrations. The HI902C also supports two dosing pumps and burettes, which the customer utilised for their sodium hydroxide titrant for acidity and silver nitrate titrant for salt determination. The HI902C in conjunction with the HI921 offers automated linked methods, which allowed the customer to measure acidity and salt sequentially in one sample. The customer appreciated the 18-beaker tray capacity of the autosampler, allowing them to designate three beakers for electrode rinsing and still run 15 samples per tray.
The customer took advantage of two of the three optional peristaltic pump inputs on the autosampler. These pumps can be used for reagent addition, deionized water addition for sample levelling, and sample aspiration into a waste container. The customer appreciated that they could measure a sample, enter the sample ID and sample size into the sample table, and simply place the sample into the autosampler tray and press “Start”. The titrator with autosampler then brings the sample to volume with deionized water, titrates for salt, titrates for acidity, and then aspirates the sample into a waste container. As each sample was titrated, the customer could view the results for both salt and acidity in the sample table. The customer appreciated that when exporting the results onto a USB flash drive, the sample table was included in an autosampler tray report as well as a report for each individual sample, for both salt and acidity. The improved accuracy and traceability of the HI902 and HI921 from their manual titrations also impressed the customer ’s existing and potential contracts, making them more competitive in the food processing market.