Offre de thèse à l'Université d'Avignon

Tout afficher

Edité le 19/11/2019

L'UMR408 Sécurité et Qualité des Produits d'Origine Végétale de l' Université d'Avignon recrute un doctorant sur le thème: Impact of cell wall and polyphenol composition on the texture of banana and yam products produced after heat processing

  • Lieu de la thèse: Avignon (south of France) ; Quality and Process team

  • PhD school: Ecole doctorale 536 Agrosciences et Sciences, Université d'Avignon.

  • Thesis co-directors: Agnès Rolland-Sabaté, Carine Le Bourvellec

  • Salaire: 1400 €/mois

  • Keywords: Cell wall analysis, pectin, banana, plantain, yam, texture, cooking ability, polyphenol, procyanidin

Context:

Strengthen the food security in South countries is necessary in particular for starchy products such as roots, tubers and
bananas (RTB) which are staple foods for South populations. Many varieties of RTB, resistant to diseases and pests or
with high carotenoid contents for eg., developed by national and international breeding programs (cassava, sweet
potato, yam, cooking banana, potato) have serious problems of acceptability and adoption by the main actors in RTB
value chains in Africa. Consumer acceptability is the key for improving the nutritional quality of RTB products. It is
therefore important to provide to breeders tools allowing them to improve the creation and selection of hybrids based on
the expected sensory quality. The thesis will be part of the “Breeding RTB products for end user preferences
(RTBfoods)” project funded by Bill and Melinda Gates Fondation which aims to identify essential quality traits for
users and consumers across a wide range of basic food products and to establish varietal selection methods of these
quality traits to meet the expectations of users. Specifically, the thesis will focus on boiled yam and banana, which are
staple food in West Africa.
Among the sensory criteria, texture is a primary quality factor for yam and banana products, followed by color, flavor
and digestibility. The texture quality of boiled yam and banana end-products depends on the initial characteristics of
raw material and on processing techniques (Otegbayo et al., 2005; Akissoe et al., 2011; Gafuma et al., 2018). Yam tuber
hardness or mealiness after boiling could be due to cell wall thickening, permeability changes of the cell wall and of the
cell adhesion (Otegbayo et al., 2005; Akissoe et al., 2011), and/or lignification-like mechanism involving phenols
(Medoua et al., 2005; Medoua et al., 2006) but the relationship with cell wall and polyphenol structure and composition
still remains to be detailed as the changes in the composition during and after cooking are only partially established.
Cooking resulted in pectin solubilisation and middle lamella dissolution leading to cell wall separation, and small pectin
size has been hypothetized to favour a softer texture of boiled banana (Qi et al., 2000), and a high initial dry matter
content a higher firmness (Gibert et al., 2010) in relation to starch gelatinization. While textural properties can be
predicted by titratable acidity and dry matter content, predictions of mealiness and adhesiveness were not efficient
(Bugaud et al., 2013) and certainly need new investigations (soluble pectic polysaccharides, and active tannins). For
banana no significant change in total phenolics was observed in the pulp after boiling with or without peel (Passo-
Tsamo et al., 2015), while regarding individual phenolic compounds, the most important change in the pulp was the
increase of ferulic acid.
Raw Banana and yam texture is probably determined by a few structural factors: dry matter, starch and cell wall
content. However there is little knowledge on the link between the texture of boiled banana and yam and the original
RTB as much information is still lacking since in most of the available literature the composition of fresh and boiled
yam and banana were evaluated separately without establish the link between them.
References:
Akissoe et al. (2011) LWT - Food Science and Technology, 44, 321-329.
Bugaud et al. (2013) Postharvest Biology and Technology, 84, 1-8.
Gafuma et al. (2018) Journal of Food Research, 7, 98-111.
Gibert et al. (2010) Journal of Food Engineering, 98, 471-479.
Medoua et al. (2005) Food Research International, 38, 143-149.
Medoua et al. (2006) Food Research International, 39, 513-518.
Otegbayo et al. (2005) Journal of Texture Studies, 36, 324-332.
Qi et al. (2000) Journal of Agriculture and Food Chemistry, 48, 4221-4226.
Passo Tsamo et al. (2015) Journal of Food Composition and Analysis, 44, 158-169.
II. Thesis objective
The aims of this PhD project are to:
1) Evaluate the impact of the cell wall polysaccharides composition, particularly of pectin structure, and polyphenol
composition on the softening during boiling of banana and yam.
2) Identify the biochemical mechanisms involved during boiling determining textural properties of banana and yam
products, and underlying the variability of response of bananas and yams during boiling, with a particular focus on
cell wall polysaccharides and procyanidins.

Profil du candidat:

The candidates must have a master degree (or equivalent) in physico-chemistry, quality of bioproducts, food sciences or
material sciences and have to be interested in bio-polymers and to be able to speak and write in English. He/she has
validated competences in one or more of the following topics: food biochemistry, physico-chemical techniques,
structural characterization, rheology.
A B1 french level is also necessary to obtain the residence permit for non-EU citizens.

How to apply:


Dead line: 6th of december 2019. Applications must be sent to: agnes.rolland-sabate@inra.fr
The application must contain the following documents:
- CV (current situation, curriculum, diplomas obtained, subject of research placement, level of English, level of French
for non-French speakers) ;
- 2 letters of appreciation, including one from the supervisor of the master course;
- Letter of motivation, adapted to the subject and showing the adaptation of the profile of the candidate to the proposed
subject.
The thesis will start the 2nd of january 2020.

 

 Postuler  Contact  Pièce jointe