Yanzhao Ren | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Yanzhao Ren. This seminar is open to the general public to attend.

Thesis Topic: Effect of High Pressure CO2 Treatment on the Moisture Sorption Isotherm and Physicochemical Properties of Beef Jerky

Seminar Abstract:

High pressure carbon dioxide (HPCD) treatment is a promising non-thermal pasteurization technique, targeting the enhancement of food safety by inactivating microorganisms without sacrificing quality. Even though this technique is effective for high moisture foods, research on products with a low water activity (a_w) is more limited. Beef jerky, as a low a_w ready-to-eat snack, has become more popular because of the growing trend of high-protein and low-carb diets. The objectives of this thesis research were to investigate the effects of HPCD treatment on the moisture sorption behavior and physicochemical properties of beef jerky.

Moisture sorption isotherms (MSIs) and monolayer water (M₀) content were determined under air and CO₂ environments at ambient pressure, as well as HPCD environment. MSI data were described mathematically by fitting into six isotherm equations. The deviation of the models used to fit the data increased under CO₂ atmosphere at ambient pressure and HPCD conditions. At ambient pressure, compared to the air environment, samples in CO₂ environment had larger a_w at a given moisture content. Under HPCD environment, the shape of MSIs changed from type II to type III and the isotherms became very steep at a_w levels of 0.73 and 0.70 at high pressures of 57 and 200 bar, respectively. Monolayer water content decreased with temperature, but pressure did not have a significant effect on M₀. Net isosteric heat of sorption in CO₂ environment is higher than air environment and the differential heat of sorption decreases when the moisture content is increased.

The effects of HPCD processing parameters, including pressure, temperature, processing time and depressurization rate, on the physiochemical properties, such as, a_w, surface color, fat content, and Warner-Bratzler shear force, of beef jerky were studied by response surface methodology (RSM). Water activity decreased after HPCD treatment and temperature showed a significant effect. In terms of surface color profile, L, a, b values increased after HPCD treatment and pressure had a significant effect on L value, no processing parameter showed a significant effect on a value, and pressure, quadratic pressure and depressurization rate showed a significant effect on b value. After HPCD treatment, fat content of beef jerky was reduced slightly with no processing parameter showing a significant effect. Warner-Bratzler shear force was either increased or decreased after HPCD treatment, and temperature had a significant effect. An optimum HPCD treatment condition, that is, pressure of 92.9 bar, temperature of 59.1˚C, processing time of 35.9 min and depressurization rate of 56.3 bar/min, was determined via the RSM model to minimize the changes in responses. The results obtained from this thesis research provide valuable information on further understanding of moisture sorption behavior during HPCD treatment that would contribute to microbial inactivation mechanism and the impact of HPCD treatment on the quality attributes of a low a_w food like beef jerky.

Yanzhao Ren – Msc with Dr. Feral Temelli