Structural changes associated with the inactivation of lipoxygenase by pulsed light

Pasteurization of fruit juices by pulsed light treatment: A review on the microbial safety, enzymatic stability, and kinetic approach to process design

Pulsed light (PL) is a polychromatic radiation-based technology, among many other non-thermal processing techniques. The microbiological lethality of the PL technique has been explored in different food matrices along with their associated mechanisms. Pasteurization of fruit juice requires a 5-log cycle reduction in the resistant pathogen in the product. The manufacturers look toward achieving the microbial safety and stability of the juice, while consumers demand high-quality juice. Enzymatic spoilage in fruit juice is also a crucial factor that needs attention. The retailers want the processed juice to be stable, which can be achieved by inactivating the spoilage enzymes and native microflora inside it. The present review argued about the potential of PL technology to produce a microbiologically safe and enzymatically stable fruit juice with a minimal loss in bioactive compounds in the product. Concise information of factors affecting the PL treatment (PLT), primary inactivation mechanism associated with microorganisms, enzymes, the effect of PLT on various quality attributes (microorganisms, spoilage enzymes, bioactive components, sensory properties, color), and shelf life of fruit juices has been put forward. The potential of PL integrated with other non-thermal and mild thermal technologies on the microbial safety and stability of fruit juices has been corroborated. The review also provides suggestions to the readers for designing, modeling, and optimizing the PLT and discusses the use of various primary, secondary kinetic models in detail that have been utilized for different quality parameters in juices. Finally, the challenges and future need associated with PL technology has been summarized.

Effect of pulsed light treatment on enzymes and protein allergens associated with their structural changes: a review

The pulsed light (PL) technique is used for food and surface decontamination widely. The sterilization effect of PL is well known and identified as the photo-chemical effect. Besides, PL is used to inactivate enzymes, reduce the immunoreactivity of proteins, and change protein function properties at a laboratory level. The current study aims to review the effect of PL on proteins by highlighting the differences between proteins in buffer solutions or food systems. Although PL is known as a non-thermal technique, most studies done on food systems, food temperature raised considerably. Therefore, PL inactivated many enzymes in buffer solution non-thermally, while mostly with a high increase in temperature of a food system. PL reduced food allergens several folds in some foods. However, immunoreactivity responses of some protein were increased after PL treatment. Also, the current study covers the conformational changes of proteins that occur because of PL treatment. Therefore, some techniques used to follow proteins structural changes such as polyacrylamide gel electrophoresis (SDS-PAGE), high-performance liquid chromatography (HPLC), Fourier-transform infrared spectroscopy (FTIR), etc. were defined. Studies reported that PL altered proteins structure differently. For example, some studies reported that PL degraded some proteins, while other studies suggested that PL aggregated proteins. Also, there were contrary results regarding α-helix and ß-sheet concentration for the treated proteins. In conclusion, some techniques, such as amino acid sequencing, specially when some small new fragments proteins appeared on SDS-PAGE, should be used to detect the effect of PL on proteins precisely.

Effect of pH on pulsed light inactivation of polyphenol oxidase

The inactivation of diverse food enzymes by pulsed light (PL) has been described before, including the inactivation of polyphenol oxidase (PPO) (at pH 6.5). Since the pH affects the conformation of enzymes, it may influence the inactivation of enzymes by PL. The aim of this work was to evaluate the effect of pH on the kinetics of the PL-inactivation and associated structural changes of a case enzyme. To this, PPO was treated by PL at different pHs (4.0-6.5) and its inactivation kinetics and changes in its structure were evaluated by spectrophotometric and spectrofluorometric methods. The inactivation proceeded faster at low pH and was highly correlated with the decrease in peak intrinsic fluorescence intensity. Phase diagrams and parameter A evolution indicated the absence of intermediate unfolded states during the course of the inactivation. No protein aggregation was detected by turbidimetry. Results indicate that although a low pH favors the PL-inactivation of PPO, the mechanism of inactivation is pH-independent. Beyond the specific outcome for PPO, the results are evidence of a general pH-independence in the mechanism of enzyme inactivation by PL in the pH range 4.0-6.5 and acidification can be a strategy to decrease treatment times during PL processing.