Research round-up: Food-grade coatings and TDLAS
We begin with research to develop and evaluate the use of food-grade film coatings to control mite infestations, without affecting the aging process and sensory properties of dry-cured hams.
Dry-cured hams may become infested with mites during the aging process. Whole dry-cured hams often take three months to two years to fully cure.
Methyl bromide is the only known available fumigant pesticide effective at controlling such an infestation. However, it will be phased out due to it being an ozone-depleting substance.
Cubes coated with xanthan gum + 20% propylene glycol and carrageenan/propylene glycol alginate + 10% propylene glycol were able to control mite infestations under laboratory conditions.
The scientists found that mites, which can lay three to five eggs per day, avoided the hams treated with the propylene glycol coating.
Tom Phillips, professor in Kansas State university's entomology department, was part of a research team led by food scientists at Mississippi State University.
Phillips and colleagues developed food-grade coatings with propylene glycol, a common food preservative, which they applied to hams before the aging process begins.
TDLAS: non-invasive technique
A group of researchers from Zhejiang Normal University in China and Umeå University in Sweden have reported a non-invasive technique for monitoring bacterial growth.
Jie Shao, associate professor at the Institute of Information Optics, Zhejiang Normal University, Jinhua, China, said: “By assessing the level of CO2 within a given closed compartment — bottle or bag — it’s possible to assess the microbial growth.”
Detection techniques based on optical spectrometry are most appealing because they’re non-invasive, boast high sensitivity, provide instant responses, and are potentially useful for assessment of bacterial growth, said the team.
“A technique referred to as ‘tunable diode laser absorption spectroscopy’ (TDLAS) is particularly suitable because it combines all of these properties with an ease of use and low cost,” said Shao.
“One major advantage TDLAS offers is its ability to achieve very low detection limits, on the order of parts per billion. Apart from concentration, it’s also possible to determine other properties of the gas under observation — temperature, pressure, velocity and mass flux.”
The group’s setup involves a tunable diode laser as the light source, beam shaping optics, a sample to be investigated, receiving optics, and one or more detectors.
When the wavelength is tuned across the transition in a specific way, it can be combined with a technique called “wavelength modulation” (WM), which gives the TDLAS technique enhanced sensitivity (WM-TDLAS.)
Campylobacter in the gut
Meanwhile, Tom Humphrey, professor of Bacteriology and Food Safety at Swansea University, was one of the researchers which examined the immune response of broiler chickens to Campylobacter jejuni.
The project was BBSRC-funded and involved the universities of Newcastle, Liverpool and Swansea.
The team looked at something called cytokines, which are messenger molecules that tell the body, which is the best way to fight an infection. They found that the immune response is similar to other animals that are fighting a bacterial infection in the gut.
The immune response protects the chicken but it allows Campylobacter to persist in the gut and contaminate the production environment through the broiler’s faeces.
Role of vegetable surface in harbouring pathogens
In another work, University of Illinois researchers studied the ability of pathogenic viruses to adhere to fresh produce surfaces.
They found a thousand-fold difference in the number of viral particles adhering to different types of leafy greens and tomatoes. The team inoculated leafy salad greens and tomatoes with a swine virus that mimics human rotavirus.
Vegetables with three-dimensional crystalline wax structures on the leaf cuticle harbored significantly fewer virus particles after rinsing. This was counterintuitive, as it was expected that small virus particles could “hide” in the rough structures of these cuticles.
Jack Juvik, U of I geneticist, said: “Viruses are literally everywhere, causing many opportunities for infection. But the information from this study can be used down the road to select or breed for varieties that might have the capacity to reduce adherence of these particles.”
The scientists have repeated the study using E. coli, but they plan to look at more vegetable varieties and pathogens in future.