Relationship between optical properties of beverages and microbial inactivation by intense pulsed light

Comparison of microbial reduction effect of intense pulsed light according to growth stage and population density of Escherichia coli ATCC 25922 using a double Weibull model

This study evaluated how the efficacy of intense pulsed light (IPL) was influenced by biological factors such as the incubation time and the population of Escherichia coli. According to the 4D value, the microorganisms in the exponential phase were more susceptible to IPL (0.51 J/cm²), while those in the stationary phase were the most resistant (0.67 J/cm²). The microorganisms in the exponential phase could have more critical DNA damage. In addition, the degree of inactivation was affected by the microbial population. When the population was 10⁹ CFU/ml, a maximum 3.4-log reduction was observed after applying IPL at 12.5 J/cm². In contrast, a population with a density of 10¹⁰ CFU/ml showed maximally 0.13-log reduction when IPL was applied at 18.7 J/cm². This large difference might have been due to cell distribution and aggregation. The study is expected to contribute to the analytical confirmation of the microbial reduction mechanism through non-thermal technologies.

Intense pulsed light for inactivating planktonic and biofilm molds in food

It has been reported that about a quarter of the world's agriculture products is unable to be consumed each year because of mold contamination, resulting in incalculable economic losses. Despite modern food technology and the various preservation techniques available, the problem of mold contamination of food is still not adequately controlled. In this study, we simulated the biofilm formed by Aspergillus niger and Penicillium glaucum in liquid and solid food in 96 well cell culture plates and polycarbonate membrane models, respectively, and investigated the fungicidal effect of IPL on planktonic and biofilm molds at three different capacitance parameters at room and refrigerator temperatures. The results show that IPL can achieve fungicidal rates of over 99% for planktonic molds and over 90% for biofilm molds, and that the smaller the capacitance, the more frequent the irradiation required to achieve the same fungicidal rate. In addition, temperature, A. niger or Penicillium glaucum have no effect on the fungicidal effect of IPL. We believe that IPL is a promising non-thermal physical sterilization technique for fungal inhibition on food surfaces.

Investigation on the effect of thermal sterilization versus non-thermal sterilization on the quality parameters of jujube juice fermented by Lactobacillus plantarum

This study aimed to evaluate the jujube juice treated by four different sterilization treatments as substrates for producing a probiotic beverage fermented by Lactobacillus plantarum (L. plantarum): sterilization by autoclaving (SA at 0.1 MPa,121 °C, and 20 min), pasteurization (PS at 85 °C/30 min), cold plasma sterilization (CPS at 700 W/120 s) and pulsed strong light sterilization (PLS at 1.0 Hz, 600 J, and 10 times), while jujube juice without sterilization treatment used as control (CK). The results showed that the growth ability of L. plantarum in jujube juice was not affected by different sterilization treatments. After SA and PS treatment, the particle size of jujube juice increased by 440.51% and 222.29%, respectively, and the reducing sugar content decreased by 33.83% and 24.51%, respectively. Compared with SA and PS, PLS and CPS were beneficial to improve the stability of jujube juice, and tartaric acid content in jujube juice was significantly increased after CPS treatment. There was no significant difference in sensory and nutritional quality between PLS treated jujube juice and control, and the color of PLS treated jujube juice was significantly better than that of the other three sterilization treatments. The research indicated that PLS treatment could be a prospective sterilization method applied in the processing of fermented jujube juice.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05358-8.

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.

Impact of factors affecting the efficacy of intense pulsed light for reducing Bacillus subtilis spores

This study investigated how the following four intense pulsed light (IPL) treatment factors affect the inactivation of Bacillus subtilis (KCCM 11,315) spores: distance between the sample and IPL lamp (8, 13, and 18 cm), pulse width (0.5, 1.3, and 2.1 ms), charging voltage (1000, 1200, and 1400 V), and processing time (10, 20, and 30 s). The results showed that all four factors considerably influenced the spore inactivation rate in different ways. Excluding processing time, which does not affect the pulse itself, the effect was largest for pulse width, followed by distance, and charging voltage. The optimal treatment condition that maximized the inactivation rate was a distance of 8 cm, a pulse width of 2.1 ms, a charging voltage of 1000 V, and a processing time of 30 s, which together produced a 6 log reduction. It revealed that individual factors need to be investigated together for achieving the optimal condition of IPL.

Inactivation of Bacillus subtilis spores at various germination and outgrowth stages using intense pulsed light

It is important to inactivate spore-forming bacteria in foods because their spores are highly resistant to various stresses. Although thermal treatment is an effective inactivation method, the associated high temperatures can cause changes in food quality. Intense pulsed light (IPL) is a nonthermal technique that can effectively improve food safety. This study evaluated the inactivation effects of IPL at various fluences on Bacillus subtilis spores. IPL treatment at a total fluence of 7.40 J/cm² resulted in a 7 log reduction, indicating the potential of IPL to effectively inactivate bacterial spores. The sensitivity of B. subtilis spores to IPL during germination and outgrowth was also measured. The resistance to the IPL increased temporarily until 1 h after the start of incubation, and then gradually decreased for longer incubation periods. This temporary increase in resistance at the early stage of incubation was attributed to the leakage of dipicolinic acid from the spores. The results also showed that the inactivation efficiency increases after 1 h pre-incubation because the numbers of vegetative cells increased with the incubation time.

Recent findings in pulsed light disinfection

Nonthermal disinfection technologies are gaining increasing interest in the field of minimally processed food in order to improve the microbial safety or to extend the shelf life. Especially fresh-cut produce or meat and fish products are vulnerable to microbial spoilage, but, due to their sensitivity, they require gentle preservation measures. The application of intense light pulses of a broad spectral range comprising ultraviolet, visible and near infrared irradiation is currently investigated as a potentially suitable technology to reduce microbial loads on different food surfaces or in beverages. Considerable research has been performed within the last two decades, in which the impact of various process parameters or microbial responses as well as the suitability of pulsed light (PL) for food applications has been examined. This review summarizes the outcome of the latest studies dealing with the treatment of various foods including the impact of PL on food properties as well as recent findings about the microbicidal action and relevant process parameters.