The risk of foodborne parasite infection is always present in the consumption of raw foods. Parasites are present all over the environment, representing a hazard for food safety in fresh produce, meat, seafood, dairy products, etc., with infection symptoms ranging from gastrointestinal discomfort to life threatening conditions. That is why parasite control capability of HPP plays a relevant role. Scientists and health authorities estimate that parasite outbreaks largely go unnoticed due to difficulties associated with detection and diagnostic techniques. As in the case of many foodborne pathogens, available scientific studies suggest that HPP is a viable way to minimize risk associated with parasites, while providing consumers the unique experience of tasting fresh foods.
Consumers seeking raw, unprocessed foods for healthier lifestyles inadvertently threaten themselves by risk associated not only with bacteria, but also with under the radar foodborne parasites. Thus, there is a current need for parasite control to ensure food safety. As with other pathogens, thermal processing is effective to eliminate foodborne parasites, in many cases at the expense of food quality. In 2018, multiple foodborne illness outbreaks associated to pathogen Cyclospora cayetanensis nearly reached 3,000 laboratory confirmed cyclosporiasis cases in the United States alone (Food Safety Magazine 2019).
Common foodborne parasites do not grow in conventional laboratory media, requiring a host organism such as humans or animals to manifest, which makes it difficult for detection. Consequently, ingestion of food contaminated by feces shed into the environment by an infected host is a common infection vehicle (Emameh and others 2018). Certain parasites develop a growth stage equivalent to bacterial spores known as “oocysts”, where thicker protein and lipid layers confer protection against external factors such as temperature variations and chemical agents (Fig. 1). In this state, parasites survive for extended periods in the soil or in produce surface that makes it difficult to trace back (Ryan and others 2018).
Nowadays, available parasite detection methodologies that guarantee food safety are laborious and time-consuming, which makes it difficult for food processers and authorities to detect and trace potential outbreak sources. This may be the case for parasite Cryptosporidium parvum, which has been frequently associated with waterborne disease outbreaks contaminated with fecal matter while foodborne outbreaks are estimated to often remain unreported (Ryan and others 2018). Nonetheless, cryptosporidiosis frequently result in large number of affected individuals where two distinct outbreaks in the UK related to salad consumption yielded 648 and 424 cases, occurring in 2012 and 2015, respectively (Ryan and others 2018).
Similarly, diagnosis in asymptomatic infected patients remains a challenge as in the case of Toxoplasma gondii and nematode (roundworm) Trichinella spp. These opportunistic parasites can remain undetected for years in muscle or brain tissue of healthy individuals, resulting in severe cardiac, neural or visual complications once the parasite manifests when the host immune system attenuates, like cancer or transplant patients (Shapiro and others 2019; Pereira and others 2010).
For seafood products, nematode Anisakis simplex (Fig. 2), is the most common human foodborne parasite (Nieuwenhuizen 2016). The infection cycle starts when infected marine mammals shed feces with Anisakis eggs into the ocean. Eggs develop into larvae, which may be ingested by crustaceans and remain in the larvae stage. Subsequently, larger fish and marine mammals consume crustaceans, where larvae develop into adult worms. In humans, ingested larvae do not develop into the adult stage. Nonetheless, consumed worms can attach to the stomach or intestinal surface, where the latter is particularly painful due to the intestine obstruction, often requiring surgery for removal (Nieuwenhuizen 2016).
Furthermore, parasite control should be a priority if we have a look at its infection symptoms in humans and foods reported in foodborne outbreaks which are summarized next.
HPP on foodborne parasite control
Literature concerning HPP technology effects on parasites is scarce, mainly attributed to challenges on laboratory detection techniques discussed in the previous section. However, reported studies suggest HPP is effective for foodborne parasites control, at relatively low pressure levels, yielding no infectivity or parasite viability at ~200-550 MPa (30,000-80,000 psi), and pressure holding times starting at 30 s (Table 2).
Relatively mild HPP conditions (~200 MPa) effectively controlled Anisakis (Table 2), representing a significant improvement and time saving safety intervention, since freezing at -20 °C for 7 days is the recommended method to eliminate the parasite (Dong and others 2003). In arrowtooth flounder and halibut, HPP conditions yielding 100% A. simplex nematode inactivation (Table 2), did not alter fish fillet color up to 7 days in refrigeration storage (Dong and others 2003).
Microscopy images of fish naturally contaminated with A. simplex larvae subjected to 200 MPa, 10 min showed no visible damage on the nematode cuticle, enlisting internal organelle breakdown and modification of inner protein as potential mechanisms (Molina-García and Sanz 2002). The authors pointed out that the apparent absence of physical damage on Anisakis cuticle can prevent leakage of allergenic components into the fish tissue. Differences in HPP conditions suggest that A. simplex larvae might be more pressure resistant when compared to the fully developed grown stage (worm).
Overall, larger sized, more complex organisms are more sensitive to high pressure effects, as consistently observed for yeasts and molds when compared to bacteria (Mañas and Pagan 2005). In the case of parasites, smaller sized oocysts exhibited increased pressure resistance when compared to nematodes and larvae that are sometimes observed at plain sight.
Parasite Cyroptospordium parvum required 550 MPa, 120 s to achieve 100% infectivity loss in apple and orange juice (Slifko and others 2000). Regarding Cyclospora, humans are the only known host for parasite C. cayetanensis, significantly hindering studies to evaluate effects of high pressure (Shearer and others 2007). Nonetheless, parasite Eimeria acervulina has been targeted as a potential surrogate, since it shows similar morphological and genetic properties with Cyclospora. Chickens administered with E. acervulina oocysts processed at 550 MPa with 120 s holding time, developed no infection symptoms (Shearer and others 2007; Kniel and others 2007).
Overall, scientific reports suggest that HPP minimized foodborne risk does not inflict severe changes in chemical compounds associated with the nutritional and organoleptic properties of foods
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