Fat content and storage conditions are key factors on the partitioning and activity of carvacrol in antimicrobial packaging

The ability of carvacrol loaded polylactic acid (PLA) films to improve ground beef preservation was assessed. The mass transfer processes of carvacrol partitioning in a food packaging system between the PLA film, headspace and food product was studied. Carvacrol release was studied on packed ground beef having a fat content of 5 or 12 % at a temperature between 5 and 30 °C and a humidity between 43 and 94 % for up to 12 days. Results showed the release rate of carvacrol from the PLA film into the headspace increased with the storage temperature while the humidity in the packaging headspace had no effect on the release rate of carvacrol from the PLA film. The fat content of ground beef has a profound effect on the partitioning of carvacrol: when the system is stored at 5 °C the carvacrol absorption in the 12 % fat ground beef was about 1.3-fold compared with the carvacrol concentration observed in 5% fat ground beef. Despite this higher carvacrol absorption in the regular beef, the PLA/carvacrol films had a stronger antimicrobial effect on the lean beef suggesting that partitioning of carvacrol into the fat phase of the beef reduced its antimicrobial activity. Results highlight the importance of considering the food matrix composition in the design of antimicrobial packaging based on natural volatile components.</p

Using particle size and fat content to control the release of Allyl isothiocyanate from ground mustard seeds for its application in antimicrobial packaging

In this study an active antimicrobial packaging based on the controlled release of Allyl isothiocyanate (AITC) from mustard seed was designed. The effect of fat content and particle size of ground mustard seeds on formation and release of AITC was investigated and the underlying mechanisms were highlighted. A smaller size of mustard particles resulted in more sinigrin conversion to AITC and a higher release of AITC in the headspace. The fat content has an important role on AITC release, a decreased fat content decreased AITC levels in the particles and increased the amount of AITC in the headspace. Based on the results of the sinigrin hydrolysis, the AITC surface exchange rate and the AITC fat solubility, an overall picture of the factors influencing the AITC release from the particles is proposed, which describes formation of AITC and its partitioning between the compartments of the particles and the headspace.</p

Multiresponse kinetic modelling of the formation, release, and degradation of allyl isothiocyanate from ground mustard seeds to improve active packaging

This study aims to describe allyl isothiocyanates (AITC) formation from enzymatic sinigrin hydrolysis in ground mustard seeds and its release and degradation in the headspace using multiresponse kinetics modelling. The mechanistic modelling of the steps involved in the packaging system consists of a set of ordinary differential equations established from bio (chemical) reaction models combined with mass transfer models. The estimated parameters consist of the accessible sinigrin fraction, rate constants of sinigrin hydrolysis, AITC degradation in the particles and headspace, and its mass transfer coefficient. The model provides a good fit to experimental results and confirms the proposed mechanism of the AITC formation, degradation, and release inside the packaging system. Fat content has significant effects on AITC formation and release rate constants, while particle sizes significantly affect accessible sinigrin in the particles. These results give an understanding of AITC's controlled release by manipulating the mustard properties to optimize antimicrobial packaging designs.</p

The effect of pore size on the diffusion of volatile antimicrobials is a key factor to preserve gelled foods

This study aimed to understand how the microstructure of gelled foods impacts the diffusion of a volatile antimicrobial compound and its efficacy at different depths from the surface. Carvacrol-loaded polylactic acid film was used to inhibit the growth of Pseudomonas fluorescens in WPI-carrageenan gels during storage at 4 °C. The diffusion of antimicrobials was increased in gels having larger average pore size. The antimicrobial efficacy of the antimicrobial packaging was dependent on the diffusion of carvacrol within the gels. The final concentration of carvacrol in the top layer was more than 4 fold higher than that in the middle layer and more than 13-fold higher than that in the bottom layer, resulting in a more effective inhibition in the top layer than those in the middle and bottom layers. Our study demonstrates the importance of considering the diffusion of antimicrobials in solid/semi-solid foods in the antimicrobial packaging design.</p

Development of a moisture-activated antimicrobial film containing ground mustard seeds and its application on meat in active packaging system

An antimicrobial cellulose acetate film containing finely ground mustard seeds was developed. The effect of the film properties on the allyl isothiocyanates (AITC) formation and release into the headspace was investigated. Less porous structure and larger thickness caused slower moisture absorption and consequently a slower AITC formation and release rate. For its application in food, the film was tested on whether the concentration of AITC was sufficient to inhibit bacterial growth in ground beef with different fat contents. The AITC concentration for the low-fat ground beef was lower in the product and higher in the headspace compared to medium fat ground beef. The shelf life was extended by 3.7 and 0.6 days for low fat and medium fat ground beef respectively. Besides a novel way to control the compounds’ release to the packaging system, this study also shows the importance of the food composition for tailoring the effective active packaging. (150 words)

Packaging design using mustard seeds as a natural antimicrobial : A study on inhibition of pseudomonas fragi in liquid medium

Pseudomonas fragi is the dominant spoilage organism in various foods, especially in spoiled milk, fish, and meats. Its growth can be inhibited by releasing allyl isothiocyanate (AITC) from ground mustard seeds in food packages. This paper aims to investigate the antimicrobial potential of ground mustard seeds against P. fragi growth and the e ectiveness of released AITC concentration from mustard seeds on microbial inhibition of the spoilage bacteria growing in the liquid medium. The AITC concentration in the headspace and the liquid medium was measured and the growth of P. fragi in the liquid medium was monitored. Depending on the concentration of AITC, not only growth was inhibited but a reduction of the total count of P. fragi was even observed. The inactivation rate (k) of P. fragi was estimated using first-order inactivation kinetics and the minimum gaseous-released AITC to inactivate P. fragi was determined. Higher AITC concentration in the headspace and liquid medium was observed when using a higher amount of ground mustard seeds and a lower food to headspace ratio. Increasing the amount of ground mustard seeds (>100 mg per 10 mL liquid medium) led to full inactivation of P. fragi in 48 hours. By using an inhibition sigmoid Emax model, the minimum gaseous-released AITC for inactivation of P. fragi in 48 hours was observed around 15 μg/L headspace. These results indicate that inhibition of the spoilage bacteria and extending the shelf life using ground mustard seeds is only possible by applying a careful design of the packaging system.</p

Modelling the effect of food composition on antimicrobial compound absorption and degradation in an active packaging

This study aims to comprehensively describe the rate of AITC release, absorption, and degradation in the packaging system by using multiresponse kinetic modelling. The effects of food composition and temperature on allyl isothiocyanates (AITC) partitioning in an antimicrobial packaging system were investigated. A higher protein content in the food caused a higher AITC concentration in the headspace, which can be explained by a lower mass transfer coefficient of AITC transfer from the headspace into the food matrix. A higher fat content in the food matrix caused a lower AITC concentration in the headspace, which can be explained by the fat stimulating AITC partitioning into the food matrix. At a lower temperature AITC is more stable in the headspace and food matrix. The results can be used to optimize the design of a packaging system with an AITC concentration tailored to the packed food product.</p

Volatile antimicrobial absorption in food gel depends on the food matrix characteristics

The aim of this study was to investigate the influence of the food microstructure on the release, absorption and partitioning of the volatile antimicrobials from antimicrobial packaging film. Carvacrol loaded polylactic acid (PLA) film was prepared and tested on a food gel model simulating products like jellies, jams and dressings. Whey protein isolate/carrageenan gels with different microstructures were prepared by varying the NaCl concentration (50–250 mM): the higher the salt concentration the lower the gel consistency. Results showed carvacrol partitioning in the gel increase at higher concentration of NaCl. A 41% increase of carvacrol absorption after 7 days was found in gels prepared with 250 mM of NaCl, compared with the gels at 50 mM NaCl. The results can be explained by the differences in gel microstructures: gels with higher NaCl concentrations showed the small WPI-containing aggregates and large pores from confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) images, in turn facilitating carvacrol absorption by proteins in the gels. The physical properties of gels revealed that gels with higher NaCl concentrations showed lower strength and water holding capacity, pointing to a more loose structure of the gel. The results demonstrate that the microstructure of gels have a clear effect on carvacrol absorption and this factor should be taken into account for designing antimicrobial packaging for the preservation of the gel-like foods.</p

Carvacrol release from PLA to a model food emulsion : Impact of oil droplet size

The effect of food structure on the release of a volatile antimicrobial from an active packaging (AP) was investigated by measuring the migration of carvacrol from a polylactic acid (PLA) film to a model food system, namely, an oil-in-water (O/W) emulsion. We aimed to understand the influence of the oil droplet size on the kinetics of carvacrol migration from the PLA film to the emulsions, on its final partitioning and antimicrobial activity. Five model systems were prepared: they had the same composition, i.e., an oil fraction of 20 wt% and an aqueous phase containing 1.5 wt % whey protein isolate, but different structures. Emulsions with the smallest oil droplets (d3,2 = 0.27 μm) absorbed a higher amount of carvacrol than emulsions with large oil droplets (d3,2 = 0.34 μm and d3,2 = 0.51 μm). Despite the higher overall carvacrol concentration, inhibition of bacterial growth was less effective in emulsions with the smallest droplet (d3,2 = 0.27 μm). This can be explained by the highest log K of carvacrol in this emulsion indicating that carvacrol partitioned more into the oil droplet phase than in the continuous phase. The current study suggests that the spatial distribution of carvacrol in the emulsion determines its actual antimicrobial effect. The combined findings of antimicrobial distribution and activity highlight the need for tailoring active packaging systems based on the physical characteristics of multiphase food matrices.</p

Stir-Frying of Chinese Cabbage and Pakchoi Retains Health-Promoting Glucosinolates

Stir-frying is a cooking method, originating from Asia, in which food is fried in small amount of very hot oil. Nowadays in many other parts of the world stir-frying is a very popular method to prepare vegetables, because it is fast and fried vegetables are tasty. However, the retention of phytochemicals like the health-beneficial glucosinolates in Brassica vegetables is less explored for stir-frying in comparison to other cooking methods. This study investigates the retention of glucosinolates in Chinese cabbage (Brassica rapa ssp. pekinensis) and pakchoi (Brassica rapa ssp. chinensis) as affected by stir-frying at various cooking durations and temperatures. Stir-frying experiments were performed at set pan temperatures ranging from 160 to 250 °C for a duration of 1 to 8 min. Results showed that aliphatic glucobrassicanapin is the most abundant glucosinolate identified in fresh Chinese cabbage and pakchoi, contributing for 48 and 63% of the total glucosinolate content, respectively, followed by glucoiberin and gluconapin. Stir-frying retains the glucosinolates even at the highest temperature applied. Such retention is explained by the quick inactivation of the glucosinolate-hydrolytic enzyme myrosinase during the first minutes of frying, and by the thermal stability of the glucosinolates at those temperature/time conditions. Moreover, due to the absence of a separate water phase, leaching losses did not occur, in contrast to what is observed when boiling Brassica vegetables. These results show that stir-frying may be a suitable health-beneficial cooking option that prevents the loss of glucosinolates