Impact of thermal processing and storage on the rheological and flavour aspects of chickpea-based systems: focus on whole chickpeas and chickpea flours

The need for an increased consumption of healthier and more sustainable food sources has been growing over the past decades. In this context, pulses, such as chickpeas, are an interesting food source due to their relatively high protein, fibre, mineral and vitamin contents and relatively low lipid content. Additionally, in combination with grains, they are considered as a more sustainable alternative for animal-based proteins. The global chickpea intake could be improved by an increased consumption of whole chickpeas or by using chickpea-derived ingredients in other food products. Chickpea flour, for example, could be used as a multifunctional food ingredient, increasing the nutritional value of a food, while simultaneously contributing to an improved food consistency. Several sensory attributes, including texture, flavour and aroma, play a key role in the acceptance of food products. Different processing steps during the preparation of chickpea flour or whole chickpeas, as well as different storage conditions can affect these sensory attributes. Thus far, the impact of thermal processing and storage on the rheological and flavour aspects of chickpea-based systems only has been limitedly studied.

In this context, the aim of this PhD study was twofold. In the first experimental part, it was aimed to investigate the impact of starch state and cell intactness on the rheological and flavour aspects of chickpea flours in water-based suspensions and instant soup. In the second experimental part, the objective was to study the impact of processing and storage conditions on volatile profiles of whole chickpeas, including the effect of storage conditions on the aroma and flavour of sterilised chickpeas. From an application point of view, industrially relevant chickpea sterilisation conditions as well as a currently existing industrial relevant instant soup recipe were used.

To get insight into the potential of chickpea flour as an ingredient in (semi-)liquid food applications, three different flour types (non-gelatinised open cell flour, pre‑gelatinised closed cell flour and pre‑gelatinised open cell flour) were compared. Rheological analysis showed that the microstructure of the flours significantly influenced their viscosifying potential. The open cell flours showed potential in hot swelling applications, while the closed cell flour could be used for nutritional improvement in food applications where thickening is not desired. The pre-gelatinised open cell flour additionally showed potential to be used in cold swelling applications. Depending on the thermal treatment (e.g. instant or pasteurised application) and the other food ingredients present, the frequently industrially used potato starch could be replaced with chickpea flours in different ratios. Moreover, untargeted headspace volatile fingerprinting showed that all different chickpea flours contained a characteristic volatile profile, which was most dominantly influenced by the presence or absence of the pre-gelatinisation step. In an instant soup application, chickpea flours interacted with some of the terpene flavours and some additional (off‑)flavours were induced. However, depending on the type of chickpea flour, a similar aroma and  flavour compared to a potato starch reference soup could be achieved.

The effect of processing conditions (soaking, cooking, sterilisation) and storage conditions (time (0−52 weeks), temperature (20−42 °C) and oxygen availability) on the headspace volatile composition of whole chickpeas was investigated. To do so, untargeted volatile headspace fingerprinting, gas chromatography – mass spectrometry – olfactometry analysis and descriptive and acceptance sensory analyses were performed. Soaking of chickpeas resulted in the production of aldehydes and alcohols, linked to an unpleasant ‘beany’ aroma, while sterilisation led to more aromatic compounds, furanoids and sulphur compounds, potentially associated with pleasant aromas. During storage, a decrease in sulphury, meat-like aromas and flavours and an increase in hay-like, green-like and potato-like flavours and aromas were observed in the sterilised chickpeas. In the fresh and stored sterilised chickpeas, a total of 40 aroma-active compounds were detected. Some of these compounds were found to be important to the flavour profile of the chickpeas, but no clear relationship could be deduced between these odorants and the sensory changes observed using the descriptive analysis. Both storage temperature and oxygen availability influenced the volatile profile of sterilised chickpeas.  At increased oxygen content more hydrocarbons, sulphur compounds and ketones where formed, while at lower oxygen content more alcohols were present. However, these differences did not largely impact the flavour and aroma of the chickpeas. The aroma acceptance of chickpeas stored in both packaging materials with different oxygen permeabilities did not change during 32 weeks of storage.  The volatile changes that occurred at elevated storage temperatures (28−42 °C) were different from those at ambient storage. This demonstrated that accelerated shelf life testing was not a suitable tool to predict the shelf life of sterilised chickpeas.

It was concluded that chickpea flours possess excellent characteristics to be used as a multifunctional ingredient in (semi-)liquid food applications, depending on the microstructure allowing to increase the viscosity when desired, while at the same time contributing to an increased nutritional value. Both processing and storage conditions were concluded to be significantly important in determining the volatile profile of whole chickpeas. Current study inspires for additional research on chickpea aroma and flavour, which could eventually result in an increased acceptance of chickpeas and therewith in a growth in global consumption.