Elsevier

Journal of Food Engineering

Volume 261, November 2019, Pages 15-25
Journal of Food Engineering

Alternative environmental friendly process for dehydration of edible Undaria pinnatifida brown seaweed by microwave hydrodiffusion and gravity

https://doi.org/10.1016/j.jfoodeng.2019.05.001Get rights and content

Highlights

  • Microwave hydrodiffusion and gravity (MHG) was used for U. pinnatifida dehydration.

  • Sequential microwave powers and time provided the required final moisture content.

  • A relevant saving energy was got with the recommended MHG dehydration method (RDM).

  • RDM led to adequate microstructural, color and antioxidant capacity properties.

  • RDM samples showed comparable features to commercially dried and rehydrated seaweed.

Abstract

The impact of the processing conditions of the edible Undaria pinnatifida brown seaweed on the dehydration and bioactive features was determined using the green microwave hydrodiffusion and gravity technology. For the alga solid phase, the corresponding dehydration and rehydration kinetics, their mathematical modelling, volumetric shrinkage, energy consumption, microscopical and colorimetric properties, phenolic content and antioxidant capacity were analyzed. Results indicated that an increase in microwave power involved a notable drop in the seaweed dehydration time. The shortest dehydration treatment to reach an adequate final moisture content (<10% dry basis) was achieved using the following sequential procedure: 300 W (5 min), 100 W (10 min), 50 W (35 min) and 25 W (90 min). This recommended process also led to short rehydration time (10 min), uniform tissue surfaces, low total color differences and adequate bioactives contents. Experimental dehydration and rehydration kinetics were adequately fitted using Page and Peleg models, respectively. Estimated energy requirements were dramatically lower when compared to conventional seaweed drying treatment.

Introduction

Removing of moisture content by thermal systems for food preservation can be carried out using solar, conventional convective air drying, ultrasound, spray-drying or freeze-drying methods, among others, have been used. Today the industry food drying demands green and sustainable environmental technologies that require short operational time and reduce energy cost (Yao, 2016). Microwave hydrodiffusion and gravity (MHG) procedure could be an eco-friendly alternative for the dehydration of raw materials, as seaweeds, in contrast to the most common traditional dehydration techniques like solar methods or conventional convective air drying. Low environmental impact and high efficiency of the dehydration process can be achieved by MHG technology related to the shortest necessary time (Ferreira et al., 2018). Despite these advantages, scarce studies on the effect of MHG on the dehydration process has been reported. In contrast, this innovative technique has been used as an alternative extraction method for recovery the liquid bioactive fraction without a low energy and resources consumption of different vegetal matrix such as algae (Pérez et al., 2014) or plants (López-Hortas et al., 2016). This solvent-free technology also allows obtaining essential oil from different citrus fruits (Boukroufa et al., 2015) or aromatic plants (Asofiei et al., 2017). MHG technology can be the response of the industrial requirements of novel process for the enhancement of extraction procedures of high-added value compounds in comparison with otherconventional processes or alternative methods such as other types of microwave, enzyme, fermentation, electric pulses, surfactant or ultrasound assisted extraction, osmotic shock or supercritical fluid extraction (Wong-Paz et al., 2017, Okolie et al., 2019). This environmentally friendly process was also studied as a possibility technology to obtain fruit juices. For example, the extraction of strawberry juice by MHG was an efficient treatment with low energy consumption (Turk et al., 2017).

The growing planet population involves increasing food requirements. This circumstance encourages the exploitation of the marine environment for supplying innovative functional foodstuff. Therefore, the marine culture of different macroalgae reveals its importance as an alternative source of seaweed. Undaria pinnatifida (Harvey) Suringar (Laminariales, Phaeophyceae) brown seaweed stands out by its importance in this sector (Rebours et al., 2014). Although the consumption of this alga, so called wakame or sea mustard, is very popular in China, Japan and Korea (Balbas et al., 2015), at present its use is widespread in others cuisines of the world. This fact is reflected in the distribution of this seaweed aquaculture farms in American, African and European regions in addition to traditional Asiatic areas (Bharathiraja et al., 2015).

U. pinnatifida has diverse biological properties derived from its different chemical compounds. The high protein level among brown algae (Tascon et al., 2015) supplies an antihypertensive effect (Hayes and Tiwari, 2015). Carbohydrate fraction is the most abundant component (43.2%) and exhibits bioactive activities with multipurpose uses with pharmaceutical, cosmetic and food application (Hong et al., 2014). Diverse biological properties were described, i.e. fucoidan presents anticoagulant, anti-inflammatory, antitumoral and antiviral activities (Choo et al., 2016). The antifungal activity of this seaweed is promoted for the fatty acids content and phenolic compounds (De Corato et al., 2017). In addition, trace elements and some essential minerals are also supplied by this raw material (Rupérez, 2002). All above-mentioned provide a brown seaweed with attractive properties to be used in a broad range of food and non-food industries. Within the food applications, this seaweed can be found in pasta or cheeses matrices, among others (del Olmo et al., 2018). Concerning the non-food field, these macroalgae can be employed as bio-adsorbent for removal of heavy metals from aqueous ecosystem (Cho et al., 2013a). The extraction of biofuels (Cho et al., 2013b) and the improvement of the solar cell technologies (Calogero et al., 2014) are bioenergy production areas where U. pinnatifida can be also successfully used.

This work describes the dehydration of the edible brown U. pinnatifida seaweed by microwave hydrodiffusion and gravity. Several conditions of microwave irradiation power-time are proposed, based on the results previously optimized for other edible brown seaweeds (López-Hortas et al., 2018). Drying kinetics, shrinkage and the corresponding modelling are provided in addition to the estimation of the energy requirements. Color characteristics, structural changes and the antioxidant activity are also determined. For further insight, a systematic study on the seaweed rehydration kinetics and the corresponding modelling was also evaluated.

Section snippets

Raw materials, sample preparation and chemicals

Fresh U. pinnatifida brown seaweed (moisture content, 91.0 ± 0.1% w.b., wet basis) was harvested by a local producer (ALGAMAR, Pontevedra, Spain) which certified the authenticity of the seaweed species. Samples collected were packed in closed plastic bags protected from light and kept at −18 °C until further use. Seaweed samples were gathered and stored the same day. All the experiments were carried out during a period of two months from the date of gathering. Sea algae were defrosted (moisture

MHG dehydration curves

The collected liquid volumes during the Undaria pinnatifida brown seaweed dehydration by MHG using a broad range of microwave powers and time are shown in Fig. 2. The drained volume and the total processing time required for the seaweed dehydration dropped with rising microwave power. Operating at the lowest tested microwave power (50 W), about 180 min were necessary to dehydrate the seaweed up to a moisture content of 13.2 ± 0.3% w.b. (wet basis), after which the liquid drainage stopped (Figs.

Conclusions

It could be concluded that microwave hydrodiffusion and gravity is a promising method not only for U. pinnatifida dehydration, but also for the recovery bioactive compounds in an eco-friendly way, saving time and energy when compared with traditional dehydration process. The shortest dehydration and rehydration time are achieved using a sequential combination of microwave power and time method for an adequate final seaweed moisture content. RDM allows U. pinnatifida dehydration preserving the

Funding

Authors are grateful to the Ministry of Economy and Competitiveness of Spain (Ref. CTM 2015-68503-R) and FEDER for financial support. L. López-Hortas thanks the Xunta de Galicia for her pre-doctoral grant (2014/2020 European Social Fund). M. Gely acknowledges Erasmus + Learning Agreement for Traineeships. M.D. Torres acknowledges to the Ministerio de Economía, Industria y Competitividad for her post-doctoral grant (IJCI-2016-27535).

Declarations of interest

None.

Acknowledgements

Fresh seaweeds were kindly supplied by Algas Atlánticas ALGAMAR, S.L. (Pontevedra, Spain).

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