Contribution à l’étude de la conservation des graines de grenade (Punica granatum L.) par déshydratation osmotique

The aim of this work was to create a complete conservation process of pomegranate seeds (Punica granatum L.). This process is essentially based on osmotic dehydration (OD), which was associated to freezing and air-drying process. Several parameters were studied to optimize the process such as osmotic solution (sucrose, glucose, and sucrose/glucose and date juice with sucrose added), temperature (30, 40, and 50°C) and state of the fruit (fresh and frozen). All these conditions were linked to seed proprieties (texture, structure, and colour). The study of osmotic dehydration parameters (water loss (WL), solids gain (SG) and weight reduction (WR)) showed that most significant changes of mass transfer took place during the first 20 min of dewatering using frozen seeds, independently of temperature and sugar type. During this period, seeds water loss was estimated at 46% in sucrose, 41% in sucrose/glucose mix, 39% in date juice, and 37% in glucose. Mass transfer was slower starting from fresh fruit but led to a higher rate of WL at the end of the process. This fact can be explained by scanning electron microscopy, which showed damage of seed cell structure after freezing. This has practical consequences in terms of the modification of seeds texture. The same process also revealed a modification of seed texture and cell structure after osmotic dehydration. Using a sucrose solution and a temperature of 50°C favoured the best mass transfer. The determination of different water fractions of seed by differential scanning calorimetry (DSC) showed that the % of frozen water decreased 3.5 times contrary the % of unfreezable water that increased 2.5 times. This favours a better seeds conservation. During osmotic dehydration, there was a non negligible leaching of natural solutes from seeds into the solution, which might have an important impact on the sensorial and nutritional value of seeds. Using only osmotic dehydration could not maintain the stability of seeds during conservation. In fact, after the osmotic process, water activity of seeds was found to be higher than 0.9, allowing to the development of microorganisms and some undesirable reactions. As a consequence, a drying of the pomegranate seeds (during four hours) was investigated at three different temperatures (40, 50, and 60 °C) with air flow rate of 2 ms-1. Prior to the drying process, seeds were osmodehydrated in a sucrose solution (55°Brix) during 20 min at 50°C. The drying kinetics and the effects of OD and air-drying temperature on antioxidant capacity, total phenolic, colour, and texture were determined. This work is a contribution to the study of physico-chemical properties of pomegranate seeds (Punica granatum L.) during freezing, osmotic dehydration and drying. After the global process, the pomegranate seed characteristics lead to new industrial developments

Encres anciennes: utilisation non conventionnelle d'aliments

peer reviewedDe tout temps l’homme utilise des pigments pour peindre. Il y a 27.000 ans déjà, près de Marseille, dans la grotte Cosquer, des fresques furent peintes par des hommes préhistoriques. Il existe deux grandes catégories de pigments et colorants: les naturels et les artificiels. La première catégories contient les pigments minéraux tels que les argiles (ocre jaune ou rouge, argile verte ou brune) mais aussi des pierres (lapis lazuli (bleu)) et les pigments organiques d’origine végétale (gaude (jaune)) ou d’origine animale (murex (pourpre). La deuxième catégorie contient les pigments et colorants artificiels issus de réactions chimiques (minium (orange)) ou bien des mi-végétaux, mi-minéraux comme les encres ferro-galliques classés dans les divers. Après avoir servi pendant plusieurs siècles, tous ces pigments ont été remplacés à la fin du XIXe par des colorants synthétiques issus de la pétrochimie, car ces derniers ont l'avantage de la reproductibilité constante des couleurs. Mais la fin programmée du pétrole suscite un regain d'intérêt pour les préparations naturelles. C'est donc très logiquement que notre laboratoire a décidé de s'intéresser au sujet et en particulier aux encres venant du jus de chou rouge et aux encres ferro-grenadiques en collaboration avec l'Abbaye de Villers-la-Ville

OSMOTIC DEHYDRATION OF POMEGRANATE SEEDS (PUNICA GRANATUM L.): EFFECT OF FREEZING PRE-TREATMENT

The osmotic dehydration of pomegranate seeds was compared using fresh and frozen seeds. The process was carried out at 50C in a 55°Brix solution of sucrose. Freezing pomegranate seeds before osmotic dehydration involved an increase of effective diffusivity and a reduction in dehydration time. The most significant changes of water loss (WL) (46 g/100 g of fresh seeds [FS]) and solids gain (SG) (7 g/100 g of FS) took place during the first 20 min for frozen seeds. After this period, seeds WL and SG ranged on average close to 43 and 8 g/100 g of FS, respectively. Osmotic dehydration was slower starting from fresh fruits but led to a higher rate of WL (62 g/100 g of FS) at the end of the process. Both scanning electron microscopy and texture analysis showed a destruction of cell structure and seed texture during the pretreatment (freezing). The same techniques also revealed a texture/structure modification induced by the osmotic dehydration proces

Physico-chemical properties and amino acid profiles of sap from Tunisian date palm

Date palm sap (Phoenix dactylifera L.), also known as “legmi”, is a fresh juice extracted from date palm trees. The present study aimed to elucidate the effects of collection time (at the beginning of the tapping period and after seven days of collection) on the amino acid profile and physico-chemical properties of date palm sap from both male and female trees. Dry matter, protein, amino acid, and sugar profiles were determined using the Kjeldahl method, High-Performance Liquid Chromatography (HPLC), and High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD), respectively. Date palm sap from both male and female trees contained high levels of carbohydrates. HPLC analysis showed that this fraction was dominated by sucrose in the sap sample from female trees compared to that from male trees. Male date palm sap was noted to exhibit lower dry matter content than female date palm sap but higher protein, total polyphenol, ash, and amino acid contents. While the major essential amino acids in the sap from male trees consisted of valine and threonine, they were represented by lysine and phenylalanine in sap samples from female trees. Further, Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) analysis showed the presence of a proteinic band of 30 kDa only for the sap from male trees. Taken together, the sap from both male and female date palm trees had a number of properties that are highly valued by the functional food industry

Effect of pear apple and date fibres incorporation on the physico-chemical, sensory, nutritional characteristics and the acceptability of cereal bars

Cereal bars are nutritious food composed of several ingredients including dry raw and agglutinative ingredients. The objective of this study was to evaluate the effect of pear apple and date fibres, from cooked fruit co-product, addition on the physico-chemical textural and sensory properties of cereal bars. First, five formulations containing an amount of 10% of co-products and commercial fibre, used as a reference, were elaborated and their physico-chemical composition was determined. Second, to determine the acceptability of consumer, apple fibre co-products were added (6, 10 and 14%). Products were evaluated for their texture using a texturometer and sensory characteristics using an acceptance test. Results showed that physico-chemical composition of cereal bars elaborated with co-products was slightly different compared to those elaborated with commercial fibre. All bars have low water activity levels (∼0.470) and interesting energy (300 kcal/100 g bar). External appearance revealed a darker colour (L*:∼42/a*:∼8/b*:∼20). There were no significant differences (P > 0.05) in texture values (hardness: 40.8 N; cohesiveness: 0.34; springiness: 0.60; chewiness: 8.30 N) between cereal bars prepared with pear co-product and wheat bran. Acceptance test confirms the formulation used for cereals bars and showed that incorporation of 10% of co-product produced cereal bars with the highest acceptability. Sensory characteristics revealed that appearance is the limiting factor for consumer acceptability, essentially for cereal bars containing pear co-product. Apple, pear and date co-products could be used successfully as a food ingredient to develop new formulations of cereal bars. © 2017, The Author(s) 2017

Fractionation of apple by-products as source of new ingredients: Current situation and perspectives

Apple (Malus sp.) is among the most processed fruit that generates high amount of wastes. Depending on processes, various by-products are available offering a great diversity of low-cost raw materials. Biorefinery processes are expected to convert them into new added-value products such as hemicelluloses, oligosaccharides and polyphenols. This paper reviews the current uses of apple by-products as source of fibre and phytochemicals with special emphasis on recent fractionation processes. Future trends and challenges of apple by-product reuse are discussed

Comparative study of alkaline extraction process of hemicelluloses from pear pomace

Hemicelluloses were produced from pear pomace using direct alkaline extraction (sodium hydroxide and hydrogen peroxide) and two-step extraction with delignification pre-treatment (acidified sodium chlorite/sodium hydroxide). The aim of the study was to compare the extraction yield, composition and physicochemical characteristics of isolated hemicelluloses by size exclusion chromatography, FTIR and thermogravimetric analyses. Solid residues were analysed in order to evaluate the effect of processes on co-products (lignins and cellulose). Delignification of material (up to 995.4 g kg−1 of original lignins) during the direct alkaline hydrogen peroxide and two-step acidified sodium chlorite/sodium hydroxide processes improved the hemicellulose extraction yield attaining up to 945.3 g kg−1. Hemicelluloses were mainly composed of xylans (xylose/glucose ratio of 4.6–16.2) and had low lignin content (53.5–61.0 g kg−1 dry matter). Those from direct sodium hydroxide extraction were composed of xylans and glucans (xylose/glucose ratio of 1.5) with high content of lignins (149.3 g kg−1 dry matter). All isolated fractions were a mixture of polymers and oligomers with a molecular mass ranging from 1710 g mol−1 to 8 870 000 g mol−1. The two-step process gave the most pure cellulose residue (799.2 g kg−1 dry matter). According to results, the direct alkaline extraction with hydrogen peroxide was a promising process for the production of pure xylose-rich hemicelluloses from pear pomace solubilizing 802.2 g kg−1 of the original hemicelluloses but induced fragmentation of hemicelluloses

Effects of Processing on the Compositions and Physicochemical Properties of Fibre Concentrate from Cooked Fruit Pomaces

This study examined the influence of applied tech- nologies namely desugaring, grinding, and bleaching on the compositions (cellulose, hemicelluloses, lignins, and pectins), physicochemical properties (water-holding capacity (WHC), swelling capacity (SWC), oil-holding capacity (OHC)) and the colour of dietary fibre (DF) during the production of fibre concentrates from unusual cooked apple and pear pomaces. Thermogravimetric analysis (TGA) and optical microscopy were also performed to monitor process-induced modifica- tion. All the processing conditions affected the compositions and physicochemical properties of DF. The bleaching treat- ment induced the greatest changes on DF producing yellow cellulose-rich fibre concentrates with improved WHC from 3.2 to 10.0 g/g and improved SWC from 4.0 to 8.8 ml/g. Otherwise, reduction of the particle size influenced hydration properties and colours of DF. WHC and SWC tended to increase with the particle size whereas smaller granulometric size increased the lightness of fibres. Desugaring increased the DF content in both pomaces by 1.2-fold with slight modifica- tion of apple insoluble dietary fibre ratio. Fibre concentrates had improved WHC and SWC up to 1.4-fold. All processes had no significant effect (p < 0.05) on OHC of DF except with ultrafine apple fibre concentrates. Results showed that pro- cessing had overall positive effects on DF contents and hy- dration properties of pomaces from cooked fruits. Bleached fibre concentrates from apple pomace had the highest WHC (10.0 g/g) whereas that of pear had the highest fibre content (89.9 %). Fibres from cooked fruit pomaces may therefore be used as textural ingredients or functional foods

Synthesis of knowledge about osmotic dehydration

Parmi les procédés de conservation des produits végétaux, la déshydratation osmotique présente un intérêt économique et nutritionnel certain. Cette technique, économe en énergie, est susceptible de prolonger la période de disponibilité des produits alimentaires et leur confère des propriétés sensorielles nouvelles et appréciées. Elle permet ainsi aux acteurs de la filière agro-alimentaire d’écouler leurs productions à de meilleurs prix et aux consommateurs d’en disposer tout au long de l’année. Cette technique est un outil facile à mettre en place, surtout dans les pays en voie de développement, en raison de son faible cout. Le présent article a pour objectif de présenter une synthèse de la littérature concernant la technique de déshydratation osmotique afin d’en rappeler les bases théoriques et pratiques, mais aussi d’en préciser les nouvelles tendances et voies de recherches récentes.Among the preservation processes of vegetal products, osmotic dehydration presents an economic and a nutritional interest. This technique consumes a low quantity of energy, prolongs the period of availability of foodstuffs, and gives new and appreciated sensory properties to products. Therefore, the producers can sell their productions at better prices and the consumers are able to consume fruits and vegetables throughout the year. This technique is very easy to set up, especially in the developing countries due to its low cost. The aim of this article is to present a synthesis of the literature concerning the osmotic dehydration technique, and also to specify the new tendencies and directions of recent research