Thermal stabilisation of cocoa fruit pulp — Effects on sensory properties, colour and microbiological stability

Abstract

To improve cocoa pulp’s shelf-life, preservation processes are necessary while maintaining the quality of the pulp. We applied pasteurisation and UHT-treatment and investigated different quality parameters: dry matter content, water activity, total soluble solids, colour and peroxidase activity. Both technologies inactivated peroxidase successfully. The colour of the pasteurised pulp was similar to the fresh, while UHT-treated pulp was more brownish. The sensory properties were investigated in detail by descriptive analysis and the identification of aroma-active volatile organic compounds. Fresh pulp revealed the highest aroma intensity for attribute unripe banana-like, whereas UHT-treated pulp scored highest in the intensity of attribute tropical fruit-like. Pasteurised pulp showed strong similarities to the fresh pulp. Fresh cocoa pulp exhibited 74 aroma-active regions identified by GC-MS/O. UHT-treated and pasteurised pulp accounted for 66 and 60 aroma-active regions, respectively. Five identified substances were only found in the fresh and pasteurised pulp, namely: δ-carene, 1-pentanol, 3-(methylthio)propanol, phenol and δ-undecalactone. Similarly, fresh and UHT-treated pulp shared ten exclusive odorants, such as decanal, geraniol, and δ-nonalactone. The pasteurised and UHT-treated pulp shared two compounds, δ–decalactone and 5-(hydroxymethyl)furfural. Furthermore, the thermally treated pulps could be stored at 4 °C and 23 °C for 24 weeks without observing a significant growth of microorganisms. The rate of non-enzymatic browning was higher in samples stored at 23 °C compared to those stored at 4 °C, leading to higher browning indices. We demonstrated that pasteurisation and ultra-high temperature treatment are suitable technologies for the stabilisation of cocoa fruit pulp. These resulted in prolonged shelf-lifes and minimal changes in the sensory prorperties of the treated pulps, characterised by a reduction in the aroma diversities. This work provides important insights for the thermal stabilisation of further side-streams.