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Procesado para la conservación de alimentos

Hiperbaric’s risk assessment for Clostridium botulinum in HPP coconut water

Tender coconut water clearly enjoys the benefits of High Pressure Processing (HPP) since color, flavor and nutritional changes induced by traditional heat preservation methods are prevented. Nonetheless, food safety concerns regarding the control of Clostridium botulinum spores by HPP in the low-acid tropical juice restrict its commercialization in some regions. Hiperbaric is conducting extensive research to evaluate C. botulinum risk in tender coconut water aiming to demonstrate that HPP is a suitable preservation technology to extend shelf life and guarantee safety of this delicate beverage.


In search of alternatives for coconut water processing

There is no doubt among consumers that fruit juices represent an excellent source of health-promoting compounds such as vitamins, minerals, or antioxidants. Squeezing the juice out of the fruit at home is probably the best way to enjoy all benefits and appreciate the delicate flavor of single varieties or unique blends. However, faster lifestyle and the need to maximize increasingly limited leisure time are boosting the demand for convenience products. The range of juices in grocery stores is becoming ever wider and this requires manufacturers to seek alternatives to extend shelf life and guarantee the safety of their products. Traditional heat pasteurization can achieve these goals, but sensory and nutritional quality is negatively affected. Fortunately, High Pressure Processing (HPP) has emerged as a minimal processing technology able to deliver safe juices with an extended shelf life under refrigeration and with identical quality attributes compared to their unprocessed homologues.

Figure 1. HPP benefits for juices & beverages
Figure 1. HPP benefits for juices & beverages

Among different juices, coconut water is probably the one that benefits most from HPP. This delicate tropical beverage is extracted from tender coconuts, harvested after 7-8 months of maturation in palm trees. Its intrinsic characteristics makes it highly perishable and susceptible to spoilage.

Therefore, raw coconut water could only be enjoyed locally in the geographical areas where the fruit grows. Subjecting the juice to a preservation step is required for distribution and commercialization all around the world. Traditional heat sterilization inactivates all spoilage microorganisms and spore-forming bacteria. Nonetheless, it drastically changes color and flavor profiles of the beverage, so bringing the refreshing taste and nutritional benefits of coconut water to the population at large was challenging until the implementation of HPP at industrial scale.

Image 1. Coco Wilson, commercial example of fresh-like HPP coconut water
Picture 1. Coco Wilson, commercial example of fresh-like HPP coconut water

Limitations for the commercialization of HPP coconut water

Back in 2011, Harmless Harvest was the first company to introduce HPP coconut water in the US market. Many other brands followed in the coming years and the minimally processed juice became popular. It was the first time in history that consumers all around the world could enjoy the unique taste and nutritional benefits of coconut water as if it were extracted from just cracked coconuts. Nonetheless, in 2015 the Food and Drug Administration (FDA) showed their concern regarding the safety of this process. In the warning letters that FDA issued to companies using HPP to preserve coconut water it was stated that HPP does not consistently achieve a 5-log reduction of Clostridium botulinum spores, which was considered the pathogen of concern in this low-acid juice. This decision forced most companies to switch from HPP to alternate processing techniques.

Indeed, HPP at the conditions normally used in the food industry (up to 600 MPa/87,000 psi, 1-6 min, 4-25 °C/39-77 °F) does not inactivate bacterial spores. Spores are structures that protect certain microorganisms against non-favorable environments. When conditions become favorable, spores can grow and represent a public health hazard. In the particular case of C. botulinum, spore germination and outgrowth is associated with the production of the lethal botulinum neurotoxin (Figure 2). Nonetheless, spores themselves are innocuous and any food product with intrinsic characteristics that prevent their growth are considered safe for consumption.

Figure 2. C. botulinum life cycle and conditions that prevent (left) and support (right) spore outgrowth
Figure 2. C. botulinum life cycle and conditions that prevent (left) and support (right) spore outgrowth

Most fruit juices are naturally acidic and have a pH below 4.6, which serves as C. botulinum control. On the other hand, tender coconut water is considered a low-acid juice (pH > 4.6). Since HPP does not inactivate bacterial spores, these could potentially grow in the tropical beverage during subsequent storage and produce the botulinum neurotoxin.

Hiperbaric’s research to evaluate safety of HPP

In light of concerns raised about the safety of HPP coconut water, Hiperbaric enrolled in 2015 in a very ambitious research project in collaboration with two world-renowned institutions: KU Leuven (Belgium) and the Quadram Institute (formerly Institute of Food Research) in the UK. Hiperbaric’s applications & food processing specialist and PhD candidate Mario González Angulo focused his research activities on the behavior of C. botulinum in HPP tender coconut water.

The first stages of his experimental work aimed to evaluate the factors with an influence in the growth of C. botulinum in tender Thai coconut water. Promising results from this work were submitted to peer-review for publication in the prestigious scientific journal Food Research International. The manuscript successfully went through the review process and the free Open Access version is now available under the title “Evaluation of factors influencing the growth of non-toxigenic Clostridium botulinum type E and Clostridium sp. in high-pressure processed and conditioned tender coconut water from Thailand” (Figure 3).

Figure 3. Open Access reference article published in Food Research International with promising results evaluating the factors with an influence in C. botulinum growth in HPP coconut water
Figure 3. Open Access reference article published in Food Research International with promising results evaluating the factors with an influence in C. botulinum growth in HPP coconut water

Results from this work suggest that other intrinsic factors apart from coconut water acidity should be considered to adequately assess the risk of growth and botulinum neurotoxin production. In the next stage of his research, Mario conducted experimental work at the Quadram Institute aiming to identify the specific factors that prevent C. botulinum spore outgrowth and botulinum neurotoxin production in coconut water. Once identified, food processors could use these as Critical Limits of a Critical Control Point into their HACCP plans. Preliminary results were presented in the European Symposium of the International Association for Food Protection, and will soon be published in an Open Access scientific journal.

Image 2. Mario González, HPP Applications Specialist and PhD candidate at Hiperbaric
Picture 2. Mario González, HPP Applications Specialist and PhD candidate at Hiperbaric

This research work is in addition to many other projects on food safety that Hiperbaric has developed and disseminated since its inception. From a more general perspective, Hiperbaric also conducts research on material engineering and on mechanical elements subjected to high pressure aiming to improve the reliability and performance of HPP units. The firm has an ambitious R&D program that allocates 10% of its sales profits, and involves in innovation activities more than 20% of its workforce among food technologists, engineers and doctors. Since Hiperbaric was born in 1999, the company has been strongly committed to promoting the talent and professional development of its employees though the implementation of different training programs and providing support for the fulfilment of doctoral dissertations of various employees.

If you wish to know more about this research or any other issue related to HPP, our specialists and doctors will be more than glad to answer your questions or doubts personally.

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