Ultraviolet light based irradiation can also be

Ultraviolet light based irradiation can also be effectively applied for microbial disinfection of different fruit and vegetable juices. UV-C light has good microcidal properties and therefore it has beneficial effects in food processing for preventing microbial contamination. The UV irradiation affects the DNA of exposed microbial caffeic acid phenethyl ester based on the formation of thymine dimer in the DNA of the microorganisms and hence the ability of microorganisms to grow is destroyed [18].
The extracts obtained from the citrus fruit residues such as orange peels also have antimicrobial properties and hence have been investigated in the present work as a supplementary approach to ultrasound. The waste products obtained during the processing of citrus fruits for juice production [19] can be a sustainable source for recovery of many important natural active ingredients. For example, significant quantum of flavanones and many polymethoxylated flavones [20] are present in the peel of Citrus fruits and these flavonoids offer significant prospective applications mainly due to the range of biological activities [21,22]. Citrus peel extracts are usually composed of citrus peel oils, which have inhibiting action on the Gram positive and Gram negative bacteria, different types of yeasts, molds and food poisoning bacteria [23]. A novel approach of using the recovered active ingredients from citrus peel wastes in combination with ultrasound for juice preservation has been attempted in the present study.

Materials and methods

Results and discussions

Scale up studies
Ultrasound in combination with ultraviolet was also investigated in the large scale operation to evaluate the effects of ultrasound–ultraviolet treatment on bacterial decontamination for the large scale liquid food systems. Combined treatment of ultrasound and ultraviolet had better microbial inactivation rate in juices as compared to ultrasound alone [74], however the overall effect on microorganism inactivation in juices with a treatment time of 15min was not sufficient and showed reduced microcidal efficiency. Increasing the ultrasound+UV exposure time to 30min induced inactivation of microorganisms to a greater extent and the desired 5log reduction was achieved. Scale up results show that the combination of ultrasound+UV treatment for an irradiation time of 30min gave rise to a more pronounced microbial inactivation effect compared to treatment carried out for 15min.
The effect of combined treatment on the shelf life was caffeic acid phenethyl ester also evaluated at the large scale processing. The obtained results have been depicted in Fig. 9. It can be seen from the figure that the combined treatment over extended period of 30min was more effective in preventing the growth of the microorganisms during the storage. The effect of combined treatment on the intrinsic and extrinsic parameters of the spinach juice has been demonstrated in Fig. 10. All the treatment approaches based on ultrasound at large scale resulted in more stable juice as compared to the untreated juice. The obtained results have demonstrated that ultrasound based hurdle treatment process could easily be optimized for produce safety and can be implemented for large scale operations.

Conclusions
The present work dealt with understanding the effect of novel non-thermal techniques based on ultrasound induced cavitation along with hurdles such as natural antimicrobials i.e. orange peel extract and UV light on variety of juices. It has been established that the hurdle techniques adopted using ultrasound were successful in inactivating the microorganisms to 5log reductions which is the mandatory level set by FDA for fruit and vegetable juices. Different microorganisms were affected to different extents using ultrasound which may be attributed to the fact that different species have different cell wall structures. An in-depth study into shelf life of the processed juice with comparison of untreated juices revealed that the quality of the processed juice was much better as compared with the untreated juices. The work, thus, also demonstrated important issues related to the non-treated juices and highlights opportunities for processing of juices using novel techniques such as ultrasound. This study is particularly important as it considers all the important factors affecting food spoilage and also the study was conducted on real food systems unlike many other ultrasound bacterial inactivation studies which were conducted in model food systems and buffers.