A new procedure to prepare transparent, colourless and low-water-soluble edible films using blood plasma from slaughterhouses

doi:10.1016/j.fpsl.2021.100639

Food Packaging and Shelf Life

Volume 28, June 2021, 100639

https://doi.org/10.1016/j.fpsl.2021.100639 Get rights and content

Highlights

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New transparent and insoluble films were prepared using blood from slaughterhouses.
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The pigments of the previously acidified plasma remain in the ethanol solution.
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The precipitated proteins form a homogeneous and compact film matrix.
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The new films showed better mechanical properties than the control films.

Abstract

Some attempts to produce films using blood plasma proteins can be found in the literature; however, due to their high solubility in water, it is usually necessary to use crosslinkers, which may entail some disadvantages. In this work, a procedure to prepare water-insoluble edible films from bovine and porcine blood plasma without using crosslinkers is described for the first time, with the objective of producing sustainable packaging materials from livestock blood. For this purpose, the blood plasma fraction was acidified and treated with ethanol to precipitate the proteins, which were solubilised in water and mixed with glycerol in order to produce a film-forming solution. The generated films were investigated to determine light absorbance, transparency, microstructure, mechanical properties and solubility at several pHs and compared with a control film prepared with untreated plasma. The new films presented in this work were completely transparent and colourless on visual inspection, in contrast to the yellowish-orange colour of the control films. Furthermore, the microstructure of these new films was more homogeneous, and therefore they showed better mechanical properties than the control film. Finally, these films were found to be highly insoluble in buffer solutions of close to neutral pH, whereas the control film was almost completely solubilised in the same buffers.

Introduction

The most common proteins that have been typically used in film and coating formulations are collagen, gelatine, corn zein, casein, whey protein, wheat gluten and soy protein (Hassan, Chatha, Hussain, Zia, & Akhtar, 2018). Protein-based films exhibit poor resistance to water, i.e. are prone to dissolve if the humidity of the medium is high enough; however, they are superior to polysaccharides in their capacity to form films with good mechanical and barrier properties (Mellinas et al., 2016).

The revalorisation of blood, or its fractions as rich protein sources, is strongly encouraged, since this co-product can be considered as one of the most problematic in the food industry due to the large amount that is generated and its high polluting power. In this sense, the use of blood plasma as a raw material for films potentially offers a way to minimise the environmental impact of blood generation while increasing the added value of blood proteins.

Elaboration and characterization of plasma protein-based films have been reported by several authors; Nuthong, Benjakul, and Prodpran (2009b) prepared films using porcine plasma previously dialyzed and lyophilized with glycerol as plasticizer. However, the films obtained showed a water solubility higher than 96 %, which is highly undesirable for applications such as food coating or packaging. The same authors made several attempts to decrease the solubility of these films by adding crosslinkers, such as caffeic acid and glyoxal; however, glyoxal is a highly toxic compound and caffeic acid could exert a negative effect on the appearance of the films produced (Nuthong, Benjakul, & Prodpran, 2009a).

Taking all this into consideration and with the intention of overcoming such problems, in this study a new procedure, in which crosslinkers or other non-food-grade chemicals are not involved, is presented for the first time. This procedure is capable of preparing totally transparent and highly water-insoluble films from both bovine and porcine plasma proteins obtained from blood generated in a local slaughterhouse. In a preliminary analysis of the physical and functional properties of these films, they were tested and compared with those of a control film prepared by the traditional method.

Section snippets

Blood plasma collection

Porcine and bovine blood was collected immediately after slaughtering from a local slaughterhouse (Asturias, Spain) and poured into 3 L plastic containers. Sodium citrate, previously added, at 2 % (w/v) was used as an anticoagulant.

Plasma was separated from the cell fraction by centrifugation for 10 min at 10,000 g and 10 °C. The plasma, which is the supernatant resulting from centrifugation, was decanted and stored at −20 °C.

Film preparation

The procedure for the preparation of the new films from bovine and

Preparation of films, visual appearance, light transmission and transparency

Fig. 1 illustrates the process of fabrication of the new blood plasma-based films. It was expected that the combination of both low pH and excess of ethanol would produce conformational changes in the plasma protein, and therefore lead to its aggregation and precipitation. In fact, after the centrifugation step, the supernatant had a clear, yellowish visual appearance, while the sediment showed a whitish aspect, which suggests that the plasma pigments and lipids were solubilised in the ethanol

Conclusions

A successful new procedure to produce films using bovine and porcine blood plasma collected from slaughterhouses was described. These new films performed significantly better in key parameters such as colour, transparency and mechanical strength when compared to other methods described previously. They also showed low solubility in buffer solutions at different pH values relevant for most food products. Furthermore, it was proven that if the plasma is treated in this way, the films produced

CRediT authorship contribution statement

Sara Álvarez: Investigation, Writing - original draft. Shihan Weng: Investigation. Carlos Álvarez: Writing - review & editing. Ismael Marcet: Conceptualization, Methodology, Writing - original draft. Manuel Rendueles: Supervision, Funding acquisition. Mario Díaz: Supervision, Funding acquisition.

Acknowledgement

This work was financially supported by the Principality of Asturias, by the project GRUPIN IDI/2018/000127.

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