One of João Trigo's works involved a technique already covered in our blog: high pressure technology.
High pressure processing (HPP) is usually used for food conservation but it may be used for other applications. In this research work, João Trigo used HPP as a means of extraction.
The work aimed to produce an extract from the pomegranate peel to add to the carrot juice and to check the chemical and microbiological differences between the juice with or without extract, as well as to evaluate the effect of different types of treatments: heat treatment, high pressure treatment and no treatment.
João’s research group found that the fortified juices had fewer mesophiles (microorganisms that thrive better in moderate temperature conditions, between 20-45ºC) and psychrophils (extremophile organisms capable of living and reproducing at low temperatures) than the non-fortified ones.
This means that juices with pomegranate extract are more stable and will have a longer shelf life than those without extract.
Another parameter evaluated by this research group was the presence of phenolic compounds, tannins and the antioxidant activity of juices with this pomegranate extract. But before we know what the results were, it is important to understand the concepts:
Phenolic Compounds
In organic chemistry, phenolic compounds are a class of chemical compounds that consist of a hydroxyl group attached directly to an aromatic hydrocarbon group. Phenolic compounds are classified as simple phenols or polyphenols, based on the number of phenol units in the molecule. Phenolic compounds are a group of non-enzymatic antioxidant molecules that fight against free radicals.When in excess, free radicals promote oxidative stress and, consequently, bring complications, such as cellular aging.
Tannins
Tannins are polyphenols found in plants, they inhibit attack on plants by vertebrate or invertebrate herbivores and also by pathogenic microorganisms. Due to their chemical structure, tannins are considered adstringent molecules, have antioxidant activity, and can combine with metal ions (which is important for pharmacological applications) and macromolecules.
Antioxidant Capacity
A molecule with antioxidant capacity is a molecule capable of inhibiting the oxidation of other molecules. In chemistry, oxidation is a chemical reaction in which occurs transference of electrons or hydrogen from a substance to an oxidizing agent, which can produce free radicals. In turn, these radicals can initiate subsequent chemical reactions that, when they occur in cells, can damage them or lead them to die. So, oxidative stress had been associated with a lot of human diseases, and antioxidants molecules are often reducing agents, such as thiols, ascorbic acid or polyphenols.
So, now that you understand these concepts better, after evaluating the presence of phenolic compounds, tannins and the antioxidant activity of juices in those pomegranate extract, researchers could find out that:
The total levels of phenolic compounds, tannins and antioxidant activity showed higher values in juices supplemented with pomegranate extract during storage, compared to juices without fortification with that extract. In addition, the addition of the extract did not affect any sensory parameters.
Pressurized juices vs thermally processed juices
Regarding storage, on the 28th day, the pressurized juices exhibited lower microbial levels compared to juices treated by heat, but the phenolic compounds, the antioxidant activity and several sensory descriptors were identical for both processing treatments.
The results obtained by the authors suggest that the application of pomegranate peel extract in pressurized carrot juices improves its microbial safety and antioxidant capacity, without harming sensory aspects.
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