Traditional and emerging technologies for strawberry processing

Field: Agricultural and Biological Sciences (Life Sciences)

Strawberry is an attractive fruit, with potential benefits to human health, due to its excellent sources of natural antioxidants, anthocyanins, flavonoids, phenolic acids, as well as nutritive compounds such as minerals, vitamins and dietary fibers. However, strawberries are extremely perishable as a consequence of tenderness and susceptibility to mechanical damage, physiological deterioration, water loss and fungal spoilage. Therefore, their stabilization after harvesting and during sub-sequent storage is critical. Storage under refrigerated conditions reduces fruit deterioration as chemical and biochemical reactions and microbial growth, which may reduce quality or shelf-life, slow down when temperature is reduced. To stabilize fruits during storage, certain processes complementary to refrigeration can be used. Traditionally, several sanitizer agents, such as chlorine and hydrogen peroxide solutions, have been used to rinse fresh fruits, with the main objective of reducing microbial contamination, therefore extending product shelf life. Ideally, preservation of foods should involve technologies that prevent undesirable microbial growth, retard quality attributes degradation, and minimize nutrient losses. Thermal treatments are conventionally used to attain such targets, due to the effectiveness of heat in killing risky microorganisms and inactivating enzymes responsible for deteriorative reactions. However, unfavorable sensorial and nutritional changes, such as color degradation, softening of tissues, vitamin losses and development of unpleasant cooked flavors, may occur due to the negative impact of heat on fruits tissues. These alterations, added to the increasing consumers demand for high-quality food standards, have launched research on alternative and/or mild processing technologies that prolong foods shelf life without the detrimental effects caused by severe heating. Therefore, there is a growing interest in the application of minimal process technologies for attaining less-perishable products, safe from a microbiological perspective, while retaining quality attributes close to the fresh characteristics. Non-thermal processes, or eventually their combinations with less severe heat treatments, are emergent challenges. The application of ozone-based technologies, ultrasounds, ultraviolet radiation and high-pressure treatments are examples of processes with potential applications in the fruit industry. Modified atmosphere package, coatings with different composition, and dehydration treatments are also promising. These processes can be a key-step applied before lowtemperature storage of fruits, such as refrigeration or freezing. One should bear in mind that refrigeration or freezing cannot improve the quality of decayed food; they can only retard deterioration. The higher the quality of the product before storage, the better expected final quality before consumption. This chapter has the main objective of providing an overview of traditional and novel thermal and non-thermal processing technologies applied to strawberries. The impact of those treatments on safety aspects from a microbiological point of view, and on quality characteristics will be discussed.