Thesis Abstract

<p>                <b>ABSTRACT&nbsp;</b></p><p>Optima preservation conditions to produce canned mangoes from three cultivars (Lippens, Kent and Keitt) were determined using lemon juice and lemongrass essential oils as natural preservatives and citric acid. Fresh mango pulp and canned mangoes were analyzed for physicochemical, microbiological and sensorial properties in order to assess the impact of the canning process. Depending on cultivars fresh mango pulp contained 437.5 to 3478.09 μg/100g (dry matters) of beta-carotene. Total sugars, ash, titratable acidity, total soluble solids and pH were ranging between 49.29-67.25%, 1.23-3.0 %, 2.43-3.65%, 17 - 18 and 3.40-3.80, respectively. Total mesophilic flora, total coliforms, yeasts and moulds counts of fresh pulp ranged from 1.8 103 - 2.5 104 CFU/g, 3.6 101- 1.6 104 and lest than 10 - 9.1 101 CFU/g, respectively. After processing of canned mangoes in sucrose syrup, levels of components changed from 320.04 - 1954.01 μg/100g for beta-carotene, 50.65-79.01% for total sugars, 0.3 - 1.06% for ash, 0.64 - 2.28% for titratable acidity and 23 – 32 Brix for total soluble solids. The pH values oscillated between 3.19 and 3.98. More than 99.98% of total mesophilic flora was destroyed; no coliforms and no yeasts and moulds were detected in the canned mangoes. From these results, the best preservatives were citric acid and lemongrass essential oil and the best pasteurization time is 10 min. Keywords Mangifera indica; Canned mangoes; Natural preservative; Nutritional and hygienic quality; Burkina faso <br></p>

Thesis Overview

<p> <b>1.1 INTRODUCTION&nbsp;</b></p><p>Mangifera indica L. (mango) is the main fruit in Burkina Faso accounting for an annual production of about 404 000 tons (PAFASP, 2015)[1]. Cultivate area for mango trees represented about 58% of the area of the national orchard (Diallo, 2010). While 20% of this production is locally processed, only 5% of fresh mangoes are exported (DGPER, 2011)[2]. Thus, mango processing is poorly diversified and is mainly in the forms of drying and nectar production. In 2011, 80% of mangoes processed in Burkina Faso is dried mainly for exportation (DGPER, 2011) [2]. Industrial processing of mango beverages is developed with semi-industrial and artisanal units processing juice/nectar and a fruit processing unit (DAFANI SA) with an average mango puree production of 400 tons per year (Arnoldus, 2009)[3]. The remaining of the production is used for local consumption. However, mango being a climacteric fruit, it is hardly conservable, causing important post-harvest losses according to environmental conditions. The lack of adequate post-harvest techniques and the low level of processing cause losses that can often reach 40 to 50% of the production (ECOWAS, 2011). Since freezing of mango fruits is not applicable, their shelf life after harvesting is between 8 to 12 days at room temperature and approximatively 25 days when stored at 8-12°C (Campbell et al., 1983; CBI, 2014)[4,5]. Canning will add value and also increase the availability of mango based products to contribute for over year food security. According to the CODEX STAN 159-1987[5] “Canned mango is the product: (a) prepared from stemmed, peeled, fresh, sound, clean and mature fruit of commercial varieties conforming to the characteristics of the fruits of Mangifera indica L.; (b) which may or may not be packed with a suitable liquid packing medium, nutritive sweeteners and other seasoning or flavoring ingredients appropriate to the product; and (c) processed by heat, in an appropriate manner, before or after being sealed in a container, in order to preserve its essential composition and quality factors.” However, in order to ensure good preservation of the final product, some processing methods use inadequate heat treatments causing the alteration of nutritional and organoleptic qualities of foods (Couvert, 2002)[7]. Other methods employing chemical additives cause some adverse reactions including allergenicity (Bourrier, 2006)[8]. The involvement of certain chemical preservatives in the outbreak of some diseases justifies the development of products with natural preservatives. For instance, the effectiveness of essential oils as natural preservatives in food has been assessed in several studies (Romeo et al. 2010; Hyldgaard et al. 2012; Witkowska et al. 2014)[9-11]. Indeed, essential oils were found to express antioxidant and antimicrobial properties against a numerous microorganisms (Bassolé et al. 2011; Helander et al. 1998)[12,13]. Several data also show that lemon juice is a natural preservative with antioxidant and acidifying properties for food preservation (Agassounon et al. 2007)[14]. Due to consumer increasing demand for natural products, the use of natural additives in food processing is an alternative to obtain natural products with long shelf life. It is therefore necessary to develop a technological process using natural preservatives to satisfy consumers, to diversify mango products and to reduce losses. This contribution uses natural preservatives and short time heat treatment to improve process and preservation of canned mangoes in syrup. <br></p><p> <b>MATERIALS AND METHODS</b></p><p><b>Mangoes used as raw materials</b>&nbsp;</p><p>Mangoes fruits from the cultivars Lippens, Kent and Keitt from Orodara, in the Western area of Burkina Faso (geographical coordinates: 11°11’00’’ N and 4°17’00’’ W; 11.183333°, - 4.283333°) were used as raw materials in the present study. Mature mango fruits were picked separately from cultivars of 100 Lippens, 150 Kent and 150 Keitt. Mangoes of each cultivar were picked from the same orchard. Samples were conditioned by cultivar in cardboard boxes and transported by car to the laboratory.&nbsp;</p><p><b>Preservative compounds&nbsp;</b></p><p>Lemon (Citrus lemon) and sucrose were bought at Zogona market in Ouagadougou, Burkina Faso. Lemongrass essential oil (LEO) was provided by the Department of Natural Substances (DSN) of IRSAT/CNRST. Citric acid was purchased from COPROCHIM laboratory.&nbsp;</p><p><b>Processing of canned mangoes</b>&nbsp;</p><p>The technology used was based on the general fruit canning diagram (BIT, 1990)[15]. Series of preliminary tests have been carried out in order to adapt the diagram to process of canned mangoes using natural preservatives. A test one was based on pH measurement with series of citric acid concentrations of e.g. 0.1%, 0.2%, 0.3%, and 0.4 % in sucrose syrup. A test two was based on pH measurement with series of lemon juice concentrations of 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5% and 1.8 % in sucrose syrup. A sensory test (taste and aroma) with a concentration series of lemongrass essential oil of 0.001%, 0.002%, 0.003% and 0.004% in the syrup allowed retaining the appropriate lemongrass essential oil concentration. As for the steam bleaching, a bleaching test, carried out at different times (2, 3, 4 and 5 min) was used to select the appropriate bleaching time. The syrup is prepared with sucrose and water at dry matter level of 40 brix. Pasteurization was carried up in boiling water using appropriate equipment for different times (5, 10 and 15 min). <br></p><p> The figure 1 shows the diagram of canned mangoes processing using natural preservatives. Mangoes fruits were ripened at room temperature for 4 - 16 days. For that mature mangoes of each cultivar (Lippens, Kent and Keitt) were sorted, washed, peeled, pitted and cut into dice shape (mean side : 25-30 mm). The cutted mango pulp was bleached at 99°C for 3 min. Then 250 g of pulp were packed in twice off glass jar (capacity: 450 ml) previously washed and decontaminated by boiling in water for 15 min. Hot sucrose syrup (80 - 85°C) at the concentration of 40 Brix was added to each jar as covering liquid. For each cultivar, four types of canned mangoes were obtained according to the composition of the syrup: canned mangoes containing syrup with citric acid at 0.3 % w/v, canned mangoes containing syrup with lemon juice at 1% v/v, canned mangoes containing syrup with lemongrass essential oil at 0.002% v/v and control canned mangoes in syrup without any preservative compound. The jars were closed and then each batch was divided into three groups for the pasteurization according to the time e.g. 5, 10 and 15 min. For canned mangoes of the Lippens cultivar, pasteurization times were 15 and 10 min. In total, 32 different samples of canned mangoes were manufactured. The samples of canned mangoes were stored for 7 days at room temperature for stabilization before analyses. <br></p><p> <b>Mangoes used as raw materials:&nbsp;</b></p><p>Mangoes fruits from the cultivars Lippens, Kent and Keitt from Orodara, in the Western area were used as raw materials in the present study. Mature mango fruits were picked separately from cultivars of 100 Lippens, 150 Kent and 150 Keitt. Mangoes of each cultivar were picked from the same orchard. Samples were conditioned by cultivar in cardboard boxes and transported by car to the laboratory.<br></p><p> <b>Physicochemical analyses sample preparation&nbsp;</b></p><p>Physicochemical analyses were performed on the pulp of fresh mangoes (3 samples) and on canned mangoes (32 samples) of the three mango cultivars. The pulps of fresh mangoes were ground in Blender Moulinex brand. Prior to analysis ground products (200 g) were packaged into sampling plastics jars and frozen at – 20°C. As for canned mangoes, they were first drained using a 0.5 mm sieve to separate mango pieces from syrup. The pulp was then ground using waring blender (Moulinex). Ground product (200g) and the syrup (150g) were packed in the sampling plastics jars and frozen at - 20°C before analysis. The syrup and the ground product were separately analyzed.</p><p> <b>Composite analysis&nbsp;</b></p><p>The dry matter (DM) was determined by difference of sample weight before and after drying at 105 ± 2°C for 24 h (NF V03- 707, 2000)[16]. Results are expressed in percentage of fresh weight (FW). The total sugar was determined by sulfuric orcinol method as described by Montreuil and Spik (1969)[17]. It is a spectrophotometric method consisting of carbohydrates acid hydrolysis, intra-molecular dehydration of oses into fufurals and condensation of furfurals with phenols to obtained colored hemi- acetals or acetals. Results are expressed in percentage of dry weight (DW). Ash content was determined by incineration at 550°C for 12h according to standard procedure (IS0 2171, 2007). The titratable acidity was determined according to AFNOR, standard method NF V05 –101 (1986)[18]. The pH was measured by homogenizing 5g of product in 25 ml of distilled water using an electronic pH meter (CONSORT P901, Belgium). The titratable acidity was expressed by citric acid equivalents by titration with 0.1N NaOH using phenolphthalein as indicator. The total soluble solid was measured using an Euromex refractometer (IFFJFP, l2001). The β-Carotene content of mango pulp and canned mango was assessed by high performance liquid chromatography as described by Somé et al. (2004)[19]. The external standard solution for calibration was prepared by mixing various quantity of β-carotene standard. Optical densities of eluted compounds were read at 450 nm. The concentration of the solution having an optical density between 0.1 and 0.9 was calculated. From these standard solutions whose concentrations have been determined accurately, precise volume was taken to obtain a final solution of 60 pmol in 20 μL. The β-carotene was extracted in mango sample with successive vortexing of 1 g of ground mango product for 2 min with 1 ml of extraction solvent consisting of heterogenous mixture of hexane/3M sodium chloride/ethanol (1/1/1). After vigorous stirring, the mixture was centrifuged at 3000 rpm-1 at -5°C, for 5 min. This process was repeated three times. The hexanic phases were then pooled. The extract (1ml) was evaporated under a stream of nitrogen. The obtained residue was re-dissolved in 1ml of acetonitrile. After micro-filtration (0.5 µm&nbsp; Millipore membrane) the sample was injected in a LC-18 Supelcosil column (Bellefonte, USA), with 25 cm in length, and 4.6 mm in diameter using a loop of 20μl. The mobile phase was a mixture of acetonitrile, dichloromethane and methanol in of proportions of 7/2/1, respectively. The elution was in an isocratic mode. During the elution, carotenoids were identified by their retention time of 6.22 min ± 0.26 compared to external standards using a Jasco UV 975 detector (Tokyo, Japon), online interfaced with a computer with an operating Software Galaxie workstation version 1.9.3.2. Results are expressed in micrograms of β-carotene to 100 g of dry matter.&nbsp;</p><p> <b>Microbiological analyses&nbsp;</b></p><p>Total microflora was quantified according to ISO 6887 (1999) [20]. Roughly 10 g of the samples were homogenized in a stomacher with 90 ml of sterile peptoned buffered water. Tenfold serial dilutions were prepared and appropriates dilutions were spread-plated for microorganisms counts. Aerobic mesophilic bacteria (AMB) were counted by cultivation on plate agar count (Liofilchem, Italy) after incubation at 30°C for 72 hours according to ISO 4833 (2006). Total coliforms were determined by cultivation on violet red bile lactose agar (Liofilchem, Italy) after incubation at 37°C for 24 h (ISO 4832, 2006)[21]. Yeasts and moulds were counted by cultivation on Sabouraud- chloramphenicol agar (Liofilchem, Italy) after incubation at 25°C for 4-5 days (ISO 7954, 1988)[22]. Results are expressed in CFU per gram of sample.</p><p> <b>Sensorial analyses</b>&nbsp;</p><p>Sensorial assays were conducted according to the ISO 11035 (1994)[23]. The evaluation concerned sensory attributes and sample acceptability. Tests were performed at the sensory laboratory of the Institute of Applied Sciences and Technologies, CNRST, Burkina Faso. Tasters had a level of education at least for secondary school. Four tests were performed on canned mango: i) 9 tasters for sensory attributes such as appearance, aroma and texture of the pieces of mango pulp and the appearance of the syrup was tested; ii) 34 tasters evaluated the acceptability according to the preservative; iii) 24 tasters evaluated the acceptability according to the duration of pasteurization; and the last iv) 24 tasters evaluated the acceptability according to the mango cultivars. The canned mangoes of each formulation were randomly placed in codified plates with three-digit code (Cochran W.G, 1957)[24] and served to each panelist. Sensory evaluation was based on comparative team tasting approach used in companies where some basic rules are followed for a rigorous evaluation protocol, blind evaluation, sample quality control, individual evaluation without interaction with the team, controlled order of sample tasting, controlled tasting condition and protocol monitoring (Rogeaux, 2015)[25]. &nbsp; &nbsp; &nbsp;<br></p><p> <b>Statistical analyses&nbsp;</b></p><p>All the physicochemical analyses were performed in triplicate. Simple statistic analysis was used to get means and standard deviations. Data obtained were submitted to analysis of variance (ANOVA) and comparisons were made by Tukey’s method (P = 0.05) using XLSTAT, version 7.5.2. Sensorial analysis was submitted interpreted using SPSS 20 software (Statitics.V2 × 86 × 64 multilingual EQUINOX) <br></p>