Violette Ducruet

Influence of the nature and treatment of starch on aroma retention

The retention of aroma compounds (d-limonene, ethyl hexanoate, octanal and 1-hexanol) on different starch matrices was measured using inverse gas chromatography. The starch materials were native, acetylated and pregelatinised corn starches, maltodextrin and extruded corn starches. The influence of the amylose content and of the physical characteristics of starch (specific area, particle shape and size) were studied. Whatever the type of starch, retention increased with the polarity of the flavour molecules in the sequence: d-limonene<ethyl hexanoate<octanal<1-hexanol. Maltodextrin appeared to be the most efficient matrix for flavour retention, followed by pregelatinised starches, extruded high-amylose starch and finally granular starches (native and acetylated starches). Retention on native starches did not follow the amylose content, unlike that on extruded starches. Specific area was the main factor, which could explain the different behaviour of samples.

Quality changes in yogurt during storage in different packaging materials

The influence of packaging polymers (polypropylene or polystyrene) on the sensory and physicochemical characteristics of flavoured stirred yogurts with either 0% or 4%-fat content was investigated during the 28 days of storage at 4°C. Regardless of the packaging type, complex viscosity and thickness perception increased during storage due to exopolysaccharide production, whereas the pH of yogurts decreased. Packaging type had a greater impact on 0%-fat yogurts than on 4%-fat yogurts for both sensory and physicochemical characteristics. During storage, 0%-fat yogurt conditioned in glass displayed the lowest aroma quantity decrease of the three types of packaging, in accordance with the olfactory properties. However, between the two polymer types, polystyrene packaging seemed to be preferable for limiting aroma compound losses and subsequent fruity note intensities, and for avoiding the development of odour and aroma defects. Less significant packaging effect was observed for 4%-fat yogurts.

Use of inverse gas chromatography to determine thermodynamic parameters of aroma-starch interactions.

Interactions between aroma compounds (d-limonene, ethyl hexanoate, octanal and 1-hexanol) and high amylose cornstarch were studied using inverse gas chromatography. Free energies of adsorption (deltaGa) and enthalpies of adsorption (deltaHa) of aroma compounds on starch were measured in the temperature range of 33-40 degrees C. The results showed existence of interactions between aroma compounds and starch, involving hydrogen bounds and dipole-dipole interactions. Sorption isotherms and Henrys law solubility coefficients (S) were determined at 40 degrees C. Three different shapes of isotherms were obtained according to the BET classification: type III for d-limonene, type II for ethyl hexanoate and linear for octanal and 1-hexanol.

Evolution of aroma compounds from orange juice stored in polyethylene terephthalate (PET)

The evolution of aroma compounds from orange juice made from concentrate and stored in glass, standard monolayer polyethylene terephthalate (PET 1), multilayer PET (PET 2) and plasma-treated PET (internal carbon coating) (PET 3) was investigated. Bottles were stored at room temperature (20°C) under artificial light. Volatile compounds in orange juice samples and corresponding packaging materials were analysed at zero time and after 2, 3 and 5 months of storage. After 5 months of storage, from 0.2 to 0.3% of the initial amounts of limonene and β-myrcene in the orange juice had been absorbed by the plastic packaging materials. Statistical analyses showed that the evolution of aroma compounds was strongly correlated to the duration of storage, but not to the type of packaging material. Indeed, whatever the stored orange juice samples, the same evolutions were observed, with a decrease in aldehydes and ketones, esters, aliphatic alcohols, sesquiterpene and monoterpene alcohols, and an increase in two aliphatic and monoterpene alcohols (i.e. furfural and 4-vinylguaicol). The results suggest that the losses of aroma compounds from the juice could be attributed to the high acidity of the matrix, implying acid-catalysed reactions. Finally, PET packaging materials and their corresponding oxygen permeabilities showed no correlation with the loss of aroma compounds.

Use of inverse gas chromatography with humidity control of the carrier gas to characterise aroma-starch interactions

The interactions between aroma compounds and native corn starch were studied by inverse gas chromatography (IGC). A system of humidification of the carrier gas has been set up and generated a fixed and stable relative humidity of 56±3%. The IGC system worked under pressure (2.1 bars), using starch as stationary phase without any support. This technique allowed to maintain the starch matrix with a constant water content of 10%. The specific retention volumes of volatiles (1-hexanol, 2-hexanol, octanal, ethyl hexanoate and d-limonene) were measured under dry and humid conditions. Retention was higher under humid conditions, especially for 1-hexanol. Retention indices of volatiles with various functions and carbon chain lengths were determined on starch and compared to RI on Carbowax. RI on starch increased with the carbon chain length, like on Carbowax. Retention on starch and Carbowax followed the same general order, relative to the functional group.

Sorption of aroma compounds in PET and PVC during the storage of a strawberry syrup

The sorption of 14 aroma compounds into PET and PVC was monitored during storage of a strawberry syrup for 1 year. Concentrations in the syrup and in the polymer were determined during storage and compared with previously published results obtained with glass bottles. Apparent partition coefficients between the polymer and the syrup (noted K app) were estimated from experimental kinetics without reaching equilibrium K app values and optimally identified from the kinetic data obtained between 30 and 90 days. They exhibited a similar behaviour for both polymers with values were between 2 × 10−5 and 2 × 10−3, 4 × 10−5 and 3 × 10−2, respectively, for PET and PVC. The variation of K app values in PET was mainly correlated to the polarity of tested compounds as assessed by their log P values. By contrast, the variations in K app values for PVC were mainly related to their chain lengths. Due to slightly higher partition coefficients and diffusion coefficients in PVC compared with PET, the amount of absorbed aroma was four times higher in PVC than in PET; however, the amount of absorbed aroma compounds was less than 0.1% of the initial amount present into the syrup, except for octyl butanoate. The variation in concentration in the syrup was interpreted as a combination of a degradation process and a transport process into the packaging material. Both effects were particularly noticeable for both PET and unstable aroma compounds.

Rapid discrimination of plastic packaging materials using MIR spectroscopy coupled with independent components analysis (ICA).

Plastic packaging wastes increased considerably in recent decades, raising a major and serious public concern on political, economical and environmental levels. Dealing with this kind of problems is generally done by landfilling and energy recovery. However, these two methods are becoming more and more expensive, hazardous to the public health and the environment. Therefore, recycling is gaining worldwide consideration as a solution to decrease the growing volume of plastic packaging wastes and simultaneously reduce the consumption of oil required to produce virgin resin. Nevertheless, a major shortage is encountered in recycling which is related to the sorting of plastic wastes. In this paper, a feasibility study was performed in order to test the potential of an innovative approach combining mid infrared (MIR) spectroscopy with independent components analysis (ICA), as a simple and fast approach which could achieve high separation rates. This approach (MIR-ICA) gave 100% discrimination rates in the separation of all studied plastics: polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS) and polylactide (PLA). In addition, some more specific discriminations were obtained separating plastic materials belonging to the same polymer family e.g. high density polyethylene (HDPE) from low density polyethylene (LDPE). High discrimination rates were obtained despite the heterogeneity among samples especially differences in colors, thicknesses and surface textures. The reproducibility of the proposed approach was also tested using two spectrometers with considerable differences in their sensitivities. Discrimination rates were not affected proving that the developed approach could be extrapolated to different spectrometers. MIR combined with ICA is a promising tool for plastic waste separation that can help improve performance in this field; however further technological improvements and developments are required before it can be applied at an industrial level given that all tests presented here were performed under laboratory conditions.

Chemometric tools to highlight non-intentionally added substances (NIAS) in polyethylene terephthalate (PET).

In an effort to identify non-intentionally added substances (NIAS), which is still a challenging task for analytical chemists, PET pellets, preforms and bottles were analyzed by an optimized headspace solid phase microextraction coupled to gas chromatography-mass spectrometry (HS-SPME/GC-MS). Fingerprints obtained by the proposed method were analyzed by three chemometric tools: Principal Components Analysis (PCA), Independent Components Analysis (ICA) and a multi-block method (Common Components and Specific Weights Analysis CCSWA) in order to extract pertinent variations in NIAS concentrations. Total ion current (TIC) chromatograms were used for PCA and ICA while extracted ion chromatograms (EIC) were used for CCSWA, each ion corresponding to a block. PCA managed to discriminate pellets and preforms from bottles due to several NIAS. Volatiles like 2-methyl-1,3-dioxolane, ethylene glycol, ethylbenzene and xylene were responsible for the discrimination of pellets and preforms. Less volatile compounds like linear aldehydes and phthalates were responsible for the discrimination of bottles. ICA showed more specific discriminations especially for bottles and pellets while CCSWA managed to discriminate preforms. The proposed methodology, combining HS-SPME/GC-MS with chemometric tools proved its efficiency in highlighting NIAS in PET samples in a relatively simple and fast approach compared to classical techniques.

Independent components analysis coupled with 3D-front-face fluorescence spectroscopy to study the interaction between plastic food packaging and olive oil.

Olive oil is one of the most valued sources of fats in the Mediterranean diet. Its storage was generally done using glass or metallic packaging materials. Nowadays, plastic packaging has gained worldwide spread for the storage of olive oil. However, plastics are not inert and interaction phenomena may occur between packaging materials and olive oil. In this study, extra virgin olive oil samples were submitted to accelerated interaction conditions, in contact with polypropylene (PP) and polylactide (PLA) plastic packaging materials. 3D-front-face fluorescence spectroscopy, being a simple, fast and non destructive analytical technique, was used to study this interaction. Independent components analysis (ICA) was used to analyze raw 3D-front-face fluorescence spectra of olive oil. ICA was able to highlight a probable effect of a migration of substances with antioxidant activity. The signals extracted by ICA corresponded to natural olive oil fluorophores (tocopherols and polyphenols) as well as newly formed ones which were tentatively identified as fluorescent oxidation products. Based on the extracted fluorescent signals, olive oil in contact with plastics had slower aging rates in comparison with reference oils. Peroxide and free acidity values validated the results obtained by ICA, related to olive oil oxidation rates. Sorbed olive oil in plastic was also quantified given that this sorption could induce a swelling of the polymer thus promoting migration.

Interactions of flavoured oil in-water emulsions with polylactide

Polylactide (PLA), a biobased polymer, might prove suitable as eco-friendly packaging, if it proves efficient at maintaining food quality. To assess interactions between PLA and food, an oïl in-water model emulsion was formulated containing aroma compounds representing different chemical structure classes (ethyl esters, 2-nonanone, benzaldehyde) at a concentration typically found in foodstuff (100 ppm). To study non-equilibrium effects during food shelf life, the emulsions were stored in a PLA pack (tray and lid). To assess equilibrium effects, PLA was conditioned in vapour contact with the aroma compounds at concentrations comparable to headspace conditions of real foods. PLA/emulsion interactions showed minor oil and aroma compound sorption in the packaging. Among tested aroma compounds, benzaldehyde and ethyl acetate were most sorbed and preferentially into the lid through the emulsion headspace. Equilibrium effects showed synergy of ethyl acetate and benzaldehyde, favouring sorption of additional aroma compounds in PLA. This should be anticipated during the formulation of food products.