Composition en caroténoïdes des bananes, plantains et produits alimentaires dérivés au Cameroun – Influence variétale, environnementale et des traitements de transformation

Abstract

This study was carried out within the framework of a scientific and technical collaboration between the University of Yaoundé I – Cameroon, CARBAP – Cameroon, CIRAD – France, IRAD –Cameroon and Bioversity International – France. It aimed at contributing to the improvement of knowledge on the composition of dietary carotenoids of banana and plantain pulps. It was based on the evaluation of postharvest qualities of some Musa accessions grown in Cameroon for food purposes and varietal improvement valorisation. The study focused on (i)dietary carotenoids of Musa pulps produced in two localities of agro-ecological zone IV of Cameroon, (ii)the influence of fruit filling and fruit ripening, and (iii)the effects of processing (drying and boiling) on carotenoid composition. CARBAP hosts the world’s largest on-farm Musa collection with more than 621 accessions. More than 50 Musa cultivars from a portion of the above-mentioned collection and CARBAP experimental plots were evaluated for their colour using three scales namely: IPGRI colour chart, DSM colour chart and HarvestPlus colour chart. This was done in order to identify potentially carotenoid-rich cultivars and to determine the correlation between pulp colour and their total carotenoid content determined by pectrophotometry (λ = 450, SHIMADZU UV Mini 1240). In addition, experimental plots with ten cultivars of Musa were settled in two contrasted localities namely Njombé and Ekona respectively at 80 m and 400 m altitude above sea level. Fruits of six cultivars were evaluated for their pulp colour. Their total carotenoid content was measured using spectrophotometry technique, in relation with altitude and production cycle. French sombre, Pelipita and Grande naine were monitored during on-farm fruit filling and ripening. At flowering fruits were collected at defined frequencies (every 14 days for dessert banana and plantain cultivars, and every 21 days for cooking banana). At harvest, fruits of the 2nd and 3rd hands were collected at stages 1, 3, 5, 7 and 9 of maturation. The selected pulps underwent “quartering”process, lyophilisation, and extraction of their dietary carotenoids. The carotenoids were identified and quantified using high performance liquid chromatography. For a better understanding of the influence of processing on Musa pulp carotenoid profile and content, Batard pulps were dried at a temperature less than 50°C for 48h in a Binder model 708533 electric dryer after undergoing three blanching techniques namely: boiled water application, pre-cooking and citric acid solution utilisation. Pulps were also boiled with or without their peels for 0 min, 10 min,20 min, 30 min, 40 min, 50 min and 60 min. All the cooked pulps underwent “quartering” process,lyophilisation and extraction of their dietary carotenoids. The carotenoids were identified and quantified using high performance liquid chromatography.The pulp colours varied within the same Musa group and presented significant differences in total carotenoid contents ranging from 0.18 μg / g dw to 21.67 μg / g dw. There exist correlations between the mature pulp colour measured using HarvestPlus and DSM charts and their total carotenoid content. According to the Musa groups, the variation regression models are either linear, exponential, power or polynomial with very low adjustment degrees (R2 < 0.50); thus,showing less adjusted relationships between banana pulp colors and their total carotenoid contents. However, Mbwazirume, Mnalouki, Apantu, Cantebalon horn, Mbirinyong, Bira, Hung tu, Lalalur and Senar cultivars exhibited high total carotenoid contents (> 10 μg / g dw). They could constitute 1) potential sources of food carotenoids susceptible to be valorised in the fight against vitamin A deficiency, 2) interesting potential parents for bananas and plantains breeding designed for the improvement of pulp nutritional qualities. The localities had no influence on pulp colour. However, depending on the locality, the total carotenoid content differs very significantly according to Musa type and genomic group. Altitude enabled significant increase in the total carotenoid content. Moreover, production cycle significantly influenced the pulp total carotenoid content. Banana pulp carotenoid profile showed approximately 09 detectable and quantifiable components under specific analytical conditions. They included 04 unidentified carotenoid derivatives, lutein, 13-cis β-carotene isomer, α-carotene, β-carotene and 9-cis β-carotene isomer. Generally, unidentified and identified carotenoids varied significantly during fruit filling and ripening. From flowering to harvest, almost all carotenoids are synthesized, only lutein concentration decreases. During fruit ripening, the concentrations of all carotenoids in the pulp varied significantly depending on maturation stage and banana type. However, the variation regression models are either linear, exponential, power or polynomial with very strong correlation coefficients (R2 closer to 1); thus, demonstrating more adjusted and highly robust relationships between the carotenoid content and the filling time or ripening time. The carotenoid profile of unprocessed and processed Batard pulp also showed 09 detectable and quantifiable components under specific analytical conditions. They included 04 unidentified carotenoids, lutein, 13-cis β-carotene isomer, α-carotene, β-carotene and 9-cis β-carotene isomer. Firstly, drying enabled an increase in the number of unidentified carotenoids. Secondly, it significantly decreased the lutein, α-carotene, β-carotene and total carotenoid contents. Depending on the blanching technique, losses were estimated between 71% and 96% of the initial concentration of carotenoid. However, pre-cooking resulted in better retention of identified carotenoids. Furthermore, cooking did not alter carotenoid profile of Batard pulp. Instead, it enabled a highly significant increase of unidentified carotenoids levels. Whether cooked with or without peels, α-carotene and β-carotene contents significantly decreased during cooking and exhibited after 1 hour of boiling 390 μg % fw and approximately 260 μg % g fw respectively. This study clearly indicates that banana and plantain are important potential sources of provitamin A carotenoids. It also contributes to a better understanding of the influence of altitude, production cycle, drying and boiling on carotenoid profiles and contents of banana and plantain pulps. Biochemical changes related to carotenoids during fruit filling and ripening have also been elucidated.