From waste fruit seed to lactic acid for industrial food applications

Scientists from Nanyang Technological University, Singapore (NTU Singapore) have developed a sustainable  technique for making lactic acid, by using discarded jackfruit seeds.

Lactic acid is used in the industrial production and preservation of many types of food, such as various stages of the manufacturing of bread, yoghurt, cheese, kimchi, sauerkraut and pickles. It is added to dairy products for a tangy taste, controls acidity in jams and canned fruits, and extends the shelf life of packaged meat products. In baking, it conditions dough for better texture and volume. Additionally, lactic acid helps in emulsification of dressings and sauces and maintains vibrant colours in fruits and vegetables.

Around 1.5 million metric tons of lactic acid was manufactured worldwide in 2022.

Current methods to produce lactic acid can be costly as they typically involve fermenting raw materials such as sugarcane, corn starch and beetroot sugar, which have become more expensive due to the increasing scarcity of farmland, natural disasters and rising inflation. These methods also result in large amounts of by-products, such as gypsum, which release greenhouse gases when not correctly disposed of.

The NTU-developed method is designed to be more cost-effective and sustainable than existing industrial methods as it requires fewer chemicals and processes, produces negligible amounts of by-products and reduces food waste by using unwanted jackfruit seeds.

Jackfruits are increasingly popular in diets worldwide, with its flesh often used in meat substitute applications. However, the seeds, which make up nearly a fifth of the fruit’s total weight, are most often disposed of in landfills.

Professor William Chen, Director of NTU’s Food Science and Technology (FST) program, who led the project, said: “Our jackfruit seed-based method to produce lactic acid is another success for NTU in finding new uses for products that would otherwise be left to waste. Upcycling these products to cultivate lactic acid, an indispensable component for nearly all the food we eat, is an opportunity for enhancing processing efficiency in the food supply chain, while addressing two main pressure points for the food industry — rising costs of production and waste management.”

The process uses ‘good’ bacterium

To produce lactic acid from jackfruit seeds, the NTU scientists first washed the seeds, before adding sodium hydroxide at room temperature. This is a common process to remove skins from fruits and vegetables for canning, before freeze-drying the seeds and blending them into a powder.

They then added lactiplantibacillus plantarum, a ‘good’ bacterium that is commonly found in probiotics, to the jackfruit seed powder. It takes about two days to break it down into sugars and lactic acid, the latter of which is later extracted during a filtration process.

Prof Chen added: “We are confident that our technique could become a powerful tool for manufacturing companies to produce lactic acid. On one hand, it already uses several common production techniques that are already in use in food processing facilities, such as freeze-drying, starch filtration and the extraction of lactic acid. On the other hand, the feedstock of our lactic acid is a ubiquitous unwanted product — jackfruit seeds. It has a much lower cost than current feedstocks, corn and beetroot starch, and the usage of a waste product would reflect well on corporations as they strive towards sustainability goals. A necessary difficulty, however, would be getting the jackfruit seeds to the lactic acid producers, but that could be easily addressed by making some adjustments in the food supply chain.”

The NTU team will be working on optimising their lactic acid production method to further improve its yield and quality. The researchers also plan to scale up their production process through collaborations with food and beverage partners.

The findings of the research have been published in the peer-reviewed Journal of Functional Foods.

Top image caption: (L-R) First author of the study, Tram Anh Ngoc Le, a PhD student from the Food Science and Technology (FST) program at NTU, and NTU Professor William Chen, Director of the Food Science and Technology, presenting jackfruit seeds and the lactic acid produced from the seeds. Image credit: NTU Singapore