Tara Grauwet

High pressure, thermal and pulsed electric-field-induced structural changes in selected food allergens.

SCOPE The effects of high-pressure/temperature treatment and pulsed electric field treatment on native peanut Ara h 2, 6 and apple Mal d 3 and Mal d 1b prepared by heterologous expression were examined. METHODS AND RESULTS Changes in secondary structure and aggregation state of the treated proteins were characterized by circular dichroism spectroscopy and gel-filtration chromatography. Pulsed electric field treatment did not induce any significant changes in the structure of any of the allergens. High-pressure/temperature at 20 °C did not change the structure of the Ara h 2, 6 or Mal d 3 and resulted in only minor changes in structure of Mal d 1b. Ara h 2, 6 was stable to HPP at 80 °C, whereas changes in circular dichroism spectra were observed for both apple allergens. However, these changes were attributable to aggregation and adiabatic heating during HPP. An ELISA assay of temperature treated Mal d 3 showed the antibody reactivity correlated well with the loss of structure. CONCLUSION In conclusion, novel-processing techniques had little effect on purified allergen structure. Further studies will demonstrate if these stability properties are retained in foodmatrices.

Quality changes of pasteurised orange juice during storage: A kinetic study of specific parameters and their relation to colour instability.

In view of understanding colour instability of pasteurised orange juice during storage, to the best of our knowledge, this study reports for the first time in a systematic and quantitative way on a range of changes in specific quality parameters as a function of time and as well as temperature (20-42 °C). A zero-order (°Brix, fructose, glucose), a first-order (vitamin C), a second-order (sucrose) and a fractional conversion model (oxygen) were selected to model the evolution of the parameters between parentheses. Activation energies ranged from 22 to 136 kJ mol(-1), HMF formation being the most temperature sensitive. High correlations were found between sugars, ascorbic acid, their degradation products (furfural and HMF) and total colour difference (ΔE(∗)). Based on PLS regression, the importance of the quality parameters for colour degradation was ranked relatively among each other: the acid-catalysed degradation of sugars and ascorbic acid degradation reactions appeared to be important for browning development in pasteurised orange juice during ambient storage.

Headspace components that discriminate between thermal and high pressure high temperature treated green vegetables: Identification and linkage to possible process-induced chemical changes

For the first time in literature, this study compares the process-induced chemical reactions in three industrially relevant green vegetables: broccoli, green pepper and spinach treated with thermal and high pressure high temperature (HPHT) processing. Aiming for a fair comparison, the processing conditions were selected based on the principle of equivalence. A comprehensive integration of MS-based metabolic fingerprinting techniques, advanced data preprocessing and statistical data analysis has been implemented as untargeted/unbiased multiresponse screening tool to uncover changes in the volatile fraction. For all vegetables, thermal processing, compared to HPHT, seems to enhance Maillard and Strecker degradation reaction, triggering the formation of furanic compounds and Strecker aldehydes. In most cases, high pressure seems to accelerate (an)aerobic thermal degradation of unsaturated fatty acids leading to the formation of aliphatic aldehydes and ketones. In addition, both thermal and HPHT processing accelerated the formation of sulfur-containing compounds. This work demonstrated that the approach is effective in identifying and comparing different process-induced chemical changes, adding depth to our perspective in terms of studying a highly complex chemical changes occurring during food processing.

Headspace fingerprinting as an untargeted approach to compare novel and traditional processing technologies: a case-study on orange juice pasteurisation

As a rule, previous studies have generally addressed the comparison of novel and traditional processing technologies by a targeted approach, in the sense that only the impact on specific quality attributes is investigated. By contrast, this work focused on an untargeted strategy, in order to take into account unexpected and unintended effects of (novel) processing, and to possibly uncover unknown compounds resulting from alternative processing. The potential of headspace GC-MS fingerprinting was explored as a tool to compare the impact of thermal, high pressure (HP) and pulsed electric field (PEF) processing for mild pasteurisation of orange juice. This study demonstrated that when processing conditions are selected based on equivalent microbial safety, the impact of heat, HP and PEF pasteurisation on the volatile profile of orange juice can be considered comparable. During refrigerated storage, however, indirect impact differences were revealed, which were attributed to differences in degree of enzyme inactivation.

Colour and carotenoid changes of pasteurised orange juice during storage.

The correlation of carotenoid changes with colour degradation of pasteurised single strength orange juice was investigated at 20, 28, 35 and 42°C for a total of 32 weeks of storage. Changes in colour were assessed using the CIELAB system and were kinetically described by a zero-order model. L(∗), a(∗), b(∗), ΔE(∗), Cab(∗) and hab were significantly changed during storage (p<0.05). Activation energies for all colour parameters were 64-73 kJ mol(-1). Several carotenoids showed important changes and appeared to have different susceptibilities to storage. A decrease of β-cryptoxanthin was observed at higher temperatures, whereas antheraxanthin started to decrease at lower temperatures. Depending on the time and temperature, changes in carotenoids could be due to isomerisation reactions, which may lead to a perceptible colour change. Although the contribution of carotenoids was recognised to some extent, other reactions seem of major importance for colour degradation of orange juice during storage.

High-pressure treatment reduces the immunoreactivity of the major allergens in apple and celeriac

SCOPE The impact of thermal and high pressure (HP) processing on the immunoreactivity of the allergens Mal d 1, Mal d 3 and Api g 1 has been investigated in apple and celeriac tissue, respectively. METHODS AND RESULTS The extracted proteins were assessed using SDS-PAGE and Western blot. The results showed that Mal d 1 was subject to loss of immunoreactivity as soon as the apple tissue was disrupted although it was remarkably resistant to both thermal and HP processing. This is in contrast to the Mal d 1 structural homolog from celeriac, Api g 1, that was susceptible to thermal processing. The other major allergen in apple, Mal d 3, was found to be resistant to chemical modification and thermal processing in apple, which is in contrast to behavior in solution. However, the combination of pressure and temperature significantly reduced its immunoreactivity. Pectin was found to protect Mal d 3 from thermal denaturation in solution and is a possible candidate for the protective effect of the fruit. CONCLUSION The conclusion to be drawn from these results is that the combination of HP and thermal processing is an effective method to reduce the allergenicity of both apple and celeriac.

From fingerprinting to kinetics in evaluating food quality changes

Historically, the study of food quality changes during processing, preservation, and storage has evolved from targeted, single-response studies towards studies relying on both targeted and untargeted approaches analyzing multiple responses. In our opinion, future studies should be based on a zoom-in approach in which fingerprinting is used as a multivariate, hypothesis-free starting point to screen for key quality differences in food extracts of differently processed, preserved, and stored foods. By interpreting the identity of selected fingerprint markers in terms of their relevance and consequences for application or connecting the markers to particular food reactions, in a subsequent kinetic study mechanistic as well as quantitative insight into the effect of extrinsic processing variables on quality changes can be obtained.

Effect of high pressure high temperature processing on the volatile fraction of differently coloured carrots

To get deeper insight into the effect of high pressure high temperature (HPHT) processing on the volatile fraction of carrots, differently coloured cultivars exhibiting orange, purple, red and yellow hues were investigated. The impact of HPHT sterilisation was compared with thermal sterilisation based on equivalent microbiological inactivation. The results of this study demonstrated HPHT sterilisation to exert a distinct effect on important chemical reactions in comparison to thermal sterilisation. A comprehensive integration of MS-based metabolomic fingerprinting (HS-SPME-GC-MS) and chemometric tools has been implemented as an untargeted multivariate screening tool to identify differences. In all carrot cultivars, two dominant discriminative quality-related reactions were found: oxidative degradation and the Maillard reaction. Regarding the first reaction, oxidative terpenes, free fatty acids and carotenoids degradation products were detected at higher levels after HPHT sterilisation. Regarding the latter reaction, HPHT sterilisation appeared to suppress the formation of Maillard and Strecker degradation products.

Investigating the Potential of Bacillus subtilis α-Amylase as a Pressure-Temperature-Time Indicator for High Hydrostatic Pressure Pasteurization Processes

The potential of Bacillus subtilis α‐amylase (BSA) as a pressure‐temperature‐time indicator (pTTI) for high pressure pasteurization processing (400–600 MPa; Ti 10–40°C; 1–15 min) was investigated. A stepwise approach was followed for the development of an enzyme‐based, extrinsic, isolated pTTI. First, based on literature data on the pressure stability, BSA was selected as a candidate indicator. Next to the accuracy and ease of the measurement of the indicators response (residual activity) to the pressure treatment, the storage and handling stability of BSA at atmospheric pressure was verified. Second, the stability of BSA at a constant temperature (T) and time in function of pressure (p) was investigated. Solvent engineering was used to shift the inactivation window of BSA in the processing range of interest. Third, the enzyme (1 g/L BSA—MES 0.05 M pH 5.0) was kinetically calibrated under isobaric‐isothermal conditions. Time dependent changes in activity could be modeled best by a first‐order model. Except for low pressures and high temperatures, a synergistic effect between pressure and temperature could be observed. Based on the model selected to describe the combined p,T‐dependency of the inactivation rate constant, an elliptically shaped isorate contour plot could be constructed, illustrating the processing range where BSA can be used to demonstrate temperature gradients. Fourth, the validity of the kinetic model was tested successfully under dynamic conditions similar to those used in food industry. Finally, the indicator was found suitable to demonstrate nonuniformity in two‐sectional planes of a vertical, single vessel system.

Influence of harvest maturity and fruit logistics on pineapple (Ananas comosus [L.] Merr.) volatiles assessed by headspace solid phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC/MS).

Profiling of volatiles from pineapple fruits was performed at four ripening stages using headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC/MS). In total, 142 volatiles were detected, of which 132 were identified. Multivariate data analysis was carried out to assess the effect of post-harvest storage on volatiles composition of green-ripe sea-freighted pineapple in comparison to air-freighted fruits harvested at full maturity. The latter fruits were characterised by volatiles described as potent odorants in pineapples, such as δ-octalactone, γ-lactones, 1-(E,Z)-3,5-undecatriene and 1,3,5,8-undecatetraene, as well as various methyl esters. In contrast, post-harvest storage of green-ripe sea-freighted fruits resulted in an increased formation of ethyl esters, acetates, acetoxy esters and alcohols, thus allowing the authentication of sea- and air-freighted pineapples, respectively. Particularly, compounds presumably derived from methyl-branched amino acid catabolism were identified in the fruits at later post-harvest stages. In addition, physicochemical traits were determined to characterise the fruit maturity stages.