Impact of processing on the functionalization of pumpkin pomace as a food texturizing ingredient

https://doi.org/10.1016/j.ifset.2021.102669Get rights and content

Highlights

  • Pumpkin pomace suspensions (4% w/w) possessed solid-like behavior, demonstrating structuring potential.

  • Structuring potential of pumpkin pomace was improved by heating, partial pectin removal and high pressure homogenization.

  • Storage moduli of pumpkin pomace-derived suspensions was related to swelling volume of the suspended particles.

Abstract

In the context of side-stream valorization, this study aimed to gain insight into the functionalization of industrially-generated pumpkin pomace as texturizing ingredient. Given the matrix complexity of pumpkin pomace, composed of crushed peels, seeds and mesocarp, this study focused on the impact of different sample preparation, as well as mechanical processing, on the microstructural and rheological properties of pumpkin pomace suspensions. Pumpkin pomace suspensions (4% w/w) possessed a solid-like behavior, demonstrating the potential for structure build-up. The application of heat during sample preparation (85°C, 30 min) significantly increased the storage modulus of the pumpkin pomace-derived suspensions, which was found to be related to an increased swelling volume of the suspended particles. Moreover, a combination of partial pectin removal and high pressure homogenization at 80 MPa led to improved network structure formation, as obvious from an increased storage modulus. These results are highly useful as scientific basis for exploring the texturizing potential of pumpkin pomace with minimal processing or conventional preparation methods (e.g. by heat treatment).

Introduction

With consumer demands shifting towards natural and clean-label ingredients, the food industry is showing growing interests in the valorization of agricultural by-products as potential sources of food ingredients. By targeted processing of these by-products, e.g. fruit and vegetable pomaces, they can be used to provide desirable food microstructures with optimized functional (i.e. texturizing or stabilizing) properties (Alba, Campbell, & Kontogiorgos, 2019; Moelants et al., 2014). In this context, the present study addresses the potential of pumpkin (Cucurbita sp.) pomace, obtained as industrial by-product of carotenoid extraction from pumpkin, for functionalization as texturizing ingredient.

Industrial pumpkin processing into puree, juice, etc. generates large quantities of side-streams in the form of peels, seeds and pomace (Kampuse, Ozola, Straumite, & Galoburda, 2018; Promsakha na Sakon Nakhon, Jangchud, Jangchud, & Prinyawiwatkul, 2017). When pumpkins are used for the production of food coloring agents, the pomace obtained as by-product represents a heterogeneous matrix consisting of different fractions of crushed peels, seeds and mesocarp. Today, this side-stream is utilized as animal feed (Valdez-Arjona & Ramírez-Mella, 2019), which is a low-value outlet for this by-product. Although pumpkins are not conventional sources of food fibers, several studies have investigated the functionality of polysaccharide fractions of pumpkins, focusing on the characterization of cell wall-enriched powder from residual mesocarp (de Escalada Pla, Ponce, Stortz, Gerschenson, & Rojas, 2007; Derkanosova, Vasilenko, Sokolova, Zajceva, & Ponomareva, 2018; Fissore, Ponce, Stortz, Rojas, & Gerschenson, 2007), pectic polysaccharides from peels and kernel cake (Jun, Lee, Song, & Kim, 2006; Košťálová, Aguedo, & Hromádková, 2016; Müller-Maatsch et al., 2016; Torkova et al., 2018), cell wall materials (CWM) isolated as alcohol insoluble residue (AIR) from mesocarp and milled peels (de Escalada Pla et al., 2007), and flours (Aziah & Komathi, 2009). Previous studies provided insights into the differences in composition, physicochemical and functional properties of the fiber-rich fractions prepared from pumpkins. However, with industrially-generated pumpkin pomace consisting of crushed seeds, peels and mesocarp mixed together, the raw material presents a more complex chemical composition, also being rich in proteins and lipids. The presence of these particular components can provide different properties and functionalities compared to specific isolated fractions in previous studies. A more sustainable approach would be to functionalize the pomace as such, with minimal extractions that could result in other functionalized food ingredients. To the best of our knowledge, very limited research has been conducted so far regarding the functionalization of pumpkin pomace as natural food structuring ingredient.

Technological functionalization of agricultural by-products entails creating a microstructure through a suspension of either isolated cells of the raw material and/or entangled/fragmented CWM, and analyzing the resulting rheological and functional characteristics for potential use as a food ingredient (Redgwell et al., 2008). Moelants et al. (2014) reviewed the relation between the main structural properties and the rheological behavior of plant-tissue-based food suspensions, as well as how these parameters can be directed using targeted processing. For CWM in particular, Foster (2011) and Willemsen et al. (2017) reported the improvement of rheological properties of CWM-enriched suspensions due to fiber network formation and hydration of cell wall fiber networks after tailored processing techniques (e.g. mechanical shearing and extensive pectin removal). In addition, modification of the rheological behavior of plant-based suspensions has been accomplished by changing the particle size distribution (PSD), volume fraction of particles, and particle-to-particle interactions, and concentration of insoluble fiber (Ahmed, Al-Foudari, Al-Salman, & Almusallam, 2014; Bengtsson & Tornberg, 2011; Moelants et al., 2013).

High pressure homogenization (HPH) represents a promising technique to functionalize plant-based suspensions as food structuring agents (Foster, 2011). During HPH, the coarse plant dispersion is forced through a gap in the homogenizer valve by a pressure intensifier and is subjected to intense mechanical forces and elongation stresses (Floury, Bellettre, Legrand, & Desrumaux, 2004). HPH has been demonstrated to influence the functionality of plant-based material by affecting particle dimension and morphology and/or enabling fiber network formation (Augusto, Ibarz, & Cristianini, 2012; Lopez-Sanchez et al., 2011; Van Buggenhout et al., 2015; Willemsen, Panozzo, Moelants, Wallecan, & Hendrickx, 2020). Bengtsson and Tornberg (2011) observed that HPH processing of different fruit and vegetable fiber suspensions affected the microstructure and rheological behavior in two ways: on the one hand, particle size reduction resulted in improved viscoelastic properties; while on the other hand, aggregation in the microstructure decreased the viscoelastic moduli and water-holding capacity of the fiber suspensions. Nevertheless, the impact of HPH on the functionalization of plant-based suspensions highly depends on the plant material (e.g. chemical composition, tissue type and microstructure) and on the intensity of the HPH treatment (e.g. pressure level and number of HPH passes) (Bengtsson & Tornberg, 2011; Lopez-Sanchez, Nijsse, et al., 2011; Lopez-Sanchez, Svelander, Bialek, Schumm, & Langton, 2011; Tonon, Alexandre, Hubinger, & Cunha, 2009; Van Buggenhout et al., 2015). In this context, Yu et al. (2018) and Liu et al. (2019) studied the technological (texturizing) properties of suspensions from taro pulp and lily pulp, respectively, consisting mainly of carbohydrates and proteins, and reported that HPH processing at increasing pressure levels led to changes in the macromolecular structure and interaction of proteins and starch. Moreover, changes in the physicochemical properties of structuring biopolymers, such as cellulose, pectin and proteins, have also been described in CWM from various fruit and vegetable sources subjected to HPH (Bengtsson & Tornberg, 2011; Betoret, Betoret, Rocculi, & Dalla Rosa, 2015; Willemsen et al., 2017).

The present study aimed to obtain insights into the functionalization of pumpkin pomace as a texturizing ingredient by application of (pre)processing steps. The first part focused on the preparation of different pumpkin-pomace derived samples. On the one hand, each macromolecular component (i.e. lipid, protein and starch) was selectively removed to prepare systems with reduced complexity compared to pumpkin pomace as such. On the other hand, systems composed mainly of ethanol-insoluble residues, designated as alcohol insoluble residue (AIR) and a pectin-depleted fraction derived thereof called acid insoluble residue (AR), were also prepared. The resulting chemical, microstructural and rheological properties of these suspensions were then investigated, as well as the potential of HPH on improving the rheological properties of pumpkin-pomace derived suspensions.

Section snippets

Materials and methods

Frozen pumpkin pomace from Cucurbita maxima convar. ‘Hokkaido’ (15% dry matter, pH 6.8–7.0) was provided by GNT Europa GmbH (Germany). Prior to any preparation, the pomace was thawed overnight at 4 °C. Technical ethanol was obtained from Chem-lab (Zedelgem, Belgium). Unless stated otherwise, all chemicals used were of analytical grade. The enzymes used and kits for total starch and total dietary fiber assays were supplied by Sigma-Aldrich (Diegem, Belgium) and Megazyme™ (Ireland), respectively.

Defatted, destarched, and protein-reduced pumpkin pomace samples

Compositional analysis of pumpkin pomace showed that the raw material contained, on average, 14.5% dry matter, of which 12.4% (d.b.) lipid, 10.9% (d.b.) starch, 24.4% (d.b.) protein, 42.1% (d.b.) TDF and 3.3% (d.b.) ash. The chemical composition of the prepared pumpkin pomace-derived samples is presented in Table 1. To evaluate whether the targeted macromolecular component was selectively removed from the raw material (control), the initial and residual content of each macromolecular component

Conclusion

The study evaluated the functionalization of industrially-generated pumpkin pomace as a texturizing ingredient. The present study showed that heating of pumpkin pomace (85 °C for 30 min) significantly increased G' of the pomace-derived suspensions mainly due to starch gelatinization, protein denaturation and other minor impacts of heating on the nature and components of the suspended particles. Moreover, functionalization by partial removal of pectin of the isolated AIR fraction promoted

CRediT authorship contribution statement

Sharmaine Atencio: Conceptualization, Methodology, Investigation, Validation, Formal analysis, Data curation, Writing - original draft, Writing - review & editing, Visualization. Tom Bernaerts: Conceptualization, Methodology, Investigation, Writing - review & editing, Visualization. Danyang Liu: Methodology, Investigation, Data curation, Validation. Kai Reineke: Resources, Writing - review & editing, Supervision. Marc Hendrickx: Conceptualization, Methodology, Writing - review & editing,

Declaration of Competing Interest

Authors declare no conflict of interest.

Acknowledgments

This research was financially supported by the European Union's Horizon 2020 Research & Innovation Programme under the Marie Skłodowska Curie Grant Agreement No. 765415. Tom Bernaerts is a postdoctoral researcher funded by Research Fund KU Leuven (PDM/19/128).

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