Development and characterization of a seaweed snack using Ulva fasciata

Abstract

South Asian region possess an abundant growth of seaweeds. Due to unappealing taste of seaweeds, most South Asians reject seaweed based products in the global market. Thus, the research aims to develop a seaweed snack appealing to the taste of South Asians using Ulva fasciata with the intention of popularizing seaweed consumption in the South Asia. Ulva fasciata samples were collected from Matara, Sri Lanka. Snack was developed by the traditional nori making technique. Flavor is enhanced by ginger oleoresin. The moisture content (%), total fat content (%), protein content (%) and ash content (%) of the unroasted snack was determined according to the AOAC procedures and resulted 12.52 ± 0.48, 0.26 ± 0.042, 19.18 ± 0.53 and 13.91 ± 0.46 respectively. Total carbohydrate content (%) was analyzed according to the Dubois method and recorded as 9.48 ± 0.14. The arithmetic difference was taken to determine the total fibre content (%) which was recorded as 44.64 ± 0.23. The elemental composition of the processed snack was determined by X-ray fluorescence elemental analysis. The results recorded a significantly high content (ppm) of Calcium 13,700 ± 707 in the unroasted snack. As the final outcome a nutritious seaweed snack was developed.

Introduction

Seaweeds can be introduced as a valuable marine living resources in the world. From the ancient times, these macro algae have been a source of food, feed and medicine in the east as well as in the west. (Mohammadi et al. 2013). But in South Asian region, seaweeds are an under-utilized abundant natural resource with a good potential to be utilized in the food industry. Though seaweed consumption is not popular in South Asia, edible seaweeds were widely consumed especially in other Asian countries as fresh, dried, or as ingredients in prepared foods (Ratana-arporn and Chirapart 2006). In countries like China, Korea and Japan, usage of seaweeds dated back to 2000 years. In Japan, Porphyra species is used to make “nori”. Nori is a dried sheet of seaweed used in the preparation of sushi. In countries like Malaysia and Indonesia seaweeds are widely consumed as fresh salads. The application of seaweeds in the western world was mainly related with nonfood applications. Most people around the world use seaweeds in various forms, including processed dairy, meat, and fruit products as well as domestic commodities like paint, toothpaste, solid air fresheners, cosmetics, and pharmaceutical (Tiwari and Troy 2015).

Generally, sea-vegetables are low in caloric levels, rich in vitamins, minerals and dietary fiber (Norziah and Ching 2000; Ratana-arporn and Chirapart 2006). Seaweeds are well recognized for its higher mineral composition. According to previous studies, it reveals that the mineral fraction of some seaweeds even accounts for up to 40% of dry matter and in some cases the mineral content of the seaweeds is recorded even higher than that of land plants and animal products (Rao et al. 2007). Research studies have also proved that seaweeds are also rich with antioxidants and different phytochemicals (Mohamed et al. 2012).

In recent years, global market for functional food products for human consumption has grown steadily (Hafting et al. 2012). Functional foods can be introduced as foods that have a potentially positive effect on health beyond basic nutrition. At present, consumers mostly believe that foods contribute directly for their health. Thus, they seek food not only to satisfy hunger but also to prevent nutrition-related diseases and improve physical and mental well-being. For this purpose, functional foods play an outstanding role (Siró et al. 2008). In this study, a nutritious snack is developed which can be substituted to most unhealthy snacks in South Asian markets. Most commonly people of all age groups and all income categories whether they are hungry or not consume snacks between meals. Thus their nutrient intakes apparently could be improved by introducing and popularizing nutritious and healthy snacks among people (McCoy et al. 1986). A snack is a portion of food which is often smaller than a regular meal and it is generally eaten between meals. This developed product in the research cannot be consumed as a full meal to satisfy the hunger. It can be consumed in small portions between meals. Hence, this product can be introduced as a snack. Generally, most people do not consume snacks to satisfy their hunger. They consume snacks to satisfy their craving. Thus, this study develops a nutritious snack using the seaweed variety U. fasciata. The snack is developed with 100% U. fasciata appealing to the consumers in South Asian region. Thus, the product also enables to popularize the utilization and consumption of seaweeds in the region.

Materials and methodology

Sample collection

Ulva fasciata samples required for the study were harvested manually from Mirissa, Matara, Down South, Sri Lanka [Latitude: 5°56′53.74″ (5.948262) north and Longitude: 80°28′17.71″ (80.471588) east] and transported to the laboratory in polythene bags. They were thoroughly cleaned to remove epiphytes and detritus attached to the fronds and kept in a freezer till further use.

Development of seaweed based snack

Seaweed based snack was developed from U. fasciata by the principle of traditional nori making technology. The wet sheet was oven dried for 15 h at 60 °C until a crispy sheet was obtained. Meanwhile, after 2 h of drying process a salt solution was prepared by dissolving 1.5 g of salt in 10 ml of water and sprayed on to the drying sediment. After drying process is complete, to enhance the flavor and to remove the fishy odour of seaweed based sheet, 3 ml of 200 ppm ginger oleoresin solution which was dissolved in 95% ethanol was sprayed on to the dried seaweed sheet and further oven dried for 20 min. This seaweed sheet can be consumed as a snack after roasting with oil.

Proximate analysis of the dried snack before roasting

Moisture content was determined by the infrared moisture analyzer (Shimadzu, Max 60 g, d = 0.001 g) expressed as percentage by weight of sample.

Total ash, Crude protein content, and lipid content were determined according to the standard AOAC (2000) methods. Total ash Content was determined by burning the samples in Muffle furnace at 550 °C for 6 h. Protein content was determined by the micro Kjeldahl method system (N X 6.25). Crude lipids were extracted from the powdered sample in a Soxhelt extractor with Petroleum ether as the solvent. The contents of crude lipids were determined gravimetrically after evaporating the solvent. Total carbohydrate content was determined by using modified method of Dubois et al. (1956). The standard curve for determination of total carbohydrate content was drawn for D-Glucose from regression analysis using the software MINITAB R 17 by measuring the absorbance values corresponding to D-Glucose concentration.

Total fiber content was calculated by the following equation;

$$\begin{array}{c}\%\text{Fibre content}\left(\text{m}/\text{m}\right)=100-(\text{Moisture content}+\text{Total fat}\\ +\text{Crude protein}+\text{otal carbohydrate}+\text{Total ash)}\\ \end{array}$$

Determination of mineral content of the unroasted snack

Sieved sample was compressed in a pellet press and a compressed pellet was prepared. Each compressed pellet was subjected to X-ray fluorescence emitted by XRF instrument (DX-MO8 × 045-s) in order to determine the levels of metals. Cadmium could not be detected due to the nature of the molybdenum cathode used in the instrument.

Chromameter values for snack

L*, a*, b* colour values for the fresh U. fasciata slurry and dried U. fasciata sheet were measured by using chromameter (Lovibond® LC100). Colour values were taken as replicate (n = 3) in different areas on the surface of the slurry and the sheet.

Instrumental texture analysis of the unroasted snack

Texture profile analysis (TPA) tests for the oven dried U. fasciata sheet was carried out using a computer-controlled CT3 texture analyzer (50 kg, Brookfield, USA) equipped with a 1000 g load cell. The sheet was compressed twice with a 50% deformation target using TA7 Knife edge 60 mm W probe at a pretest speed 2.00 mm/sec. The recovery time between compressions was 0 s. Two successive compressions were carried out on each sample. The resulting force–time curves were developed for hardness, chewiness, gumminess, adhesiveness, and cohesiveness. Each sample was tested 2 times at the test and return speed of 1 mm/sec. Trigger load was 10.0 g, and data rate was 20 points/ sec. Upon two compression cycles, the probe was automatically returned to the initial starting point, and the texture analyzer was reset for the next test. All analyses were conducted at ambient temperature. The same textural properties were measured for all prepared samples. All results were expressed in a report with values automatically calculated by the analyzer’s software.

Determination of the thickness of the unroasted snack

Thickness was measured by the vernier caliper with an error 0.05 mm.

Sensory evaluation for the roasted snack

A sensory evaluation was carried out to determine the best preferred roasted snack by the consumers. The effect on sensory properties such as colour, texture, taste, odour and overall acceptability with the addition of various concentrations 0, 50, 100, 200, 300 ppm of ginger oleoresin was determined by the sensory evaluation using a 5 point hedonic scale. The degree to which a product was liked was expressed as like extremely (5 points), like very much (4 points), like moderately (3 points), like slightly (2 points) and neither like nor dislike (1 point). A semi trained panel was used for the test. Nonparametric data obtained from this sensory evaluation was statistically analyzed by using Friedman test at 95% confidence level. And means separations were done by using Mann–Whitney test at 95% confidence level.

Results and discussion

In this study a snack with a thickness 0.30 ± 0.09 cm was developed. The snack was developed with U. fasciata. Salting was done during the drying process by spraying a salt solution on to the partially dried U. fasciata sheet. Ginger oleoresin was used in the latter part of the production process to enhance the flavor of the snack. Weight of a one snack is 3 g. The snack is shown in Fig. 1. According to the texture profile analysis of the unroasted seaweed snack, hardness, cohesiveness, springiness, gumminess and chewiness resulted as 0.1 N, − 5.46, 14.87 mm, − 54.6 g and − 7.99 mJ respectively. Thunyawanichnondh et al. (2020) has developed a snack from U. rigida in Thailand. Products developed by the above authors have incorporated polysaccharides but polysaccharides were not incorporated in this study. They have reported the hardness of snacks with 0.125% polysaccharide, 0.25% polysaccharide and 0.5% polysaccharide in Newton(N) as 1.09 ± 0.04, 1.74 ± 0.03 and 1.95 ± 0.05 respectively. All the snacks developed by Thunyawanichnondh et al. (2020) are harder than this snack. Among all the snacks developed by Thunyawanichnondh et al. (2020), the best preferred snack according to the sensory evaluation was the crispy seaweed supplemented with 0.25% (w/v) seaweed polysaccharide and the thickness of that snack was approximately 0.34 mm. The thickness of that snack is similar to the thickness of the snack developed in this study.

Fig. 1.

Fresh Ulva fasciata, unroasted sheet and the roasted snack. a: Ulva fasciata, b: unroasted Ulva fasciata sheet, c: Roasted Ulva fasciata snack

Sensory analysis of the roasted snack

Generally, seaweed based products in the market has a fishy odour and a fishy taste which is not appealing to the South Asian consumers. Thus, ginger oleoresin which was added as a flavor component has masked this fishy odour and taste. According to the results of the sensory analysis, P values for sensory attributes appearance, texture, odour, taste, mouth feel and overall acceptability are 0.01, 0.04, 0.017, 0.003, 0.007 and 0.000 respectively. P values are less than 0.05. Therefore, there are significant differences between all the sensory attributes and overall acceptability of the samples. According to the radar diagram (Fig. 2), odour, taste, mouth feel and overall acceptability is best for the roasted seaweed snack incorporated with 200 ppm ginger oleoresin.

Fig. 2.

Web diagram of the average rank of snacks with various concentrations of ginger oleoresin with respect to sensory attributes

Nutritional composition of the unroasted snack

Moisture, fat, protein, carbohydrate, ash and fiber in 100 g of dry weight of the snack in grams (g) are 12.52 ± 0.48, 0.26 ± 0.042, 19.18 ± 0.53, 9.48 ± 0.14, 13.91 ± 0.46 and 44.64 ± 0.23 respectively. According to the results the highest composition is comprised of fibre. Though fibre is not a nutrient it is as much as important for human health like other nutrients. Previous studies have revealed that, in comparison to the fiber content of the foods derived from terrestrial plants, seaweed has similar or even higher levels of dietary fiber. The average total dietary fiber content in seaweed can change from 36 to 60% based on its dry matter. The recommended average daily intake of dietary fiber in the United States and in the United Kingdom is about 25–30 g and more than 18 g, respectively (Rajapakse and Kim 2011). Therefore 15–17% of daily dietary requirement of fiber can be fulfilled by consuming 10 g of this snack. Generally, dietary fiber increases the fecal bulk, stimulates colonic fermentation, reduces postprandial blood glucose (reduces insulin responses) and reduces pre-prandial cholesterol levels. Hence, inclusion of fibrous foods in diets will be an added advantage to the life (Elleuch et al. 2011; Cui and Roberts 2009). The second highest composition is comprised of Proteins which equals to 19.18 ± 0.53%. This unroasted snack is also comprised of a very minute amount of fat. It is less than 1%. Generally, high fat contents accounts to high caloric levels in food. The snack is also comprised of a considerable content of ash which accounts to 13.91 ± 0.46%. That ash is consisting of a wide array of minerals which is revealed by an analysis using X-ray Fluorescence (XRF) analyzer. The results of the mineral analysis in tabulated in the Table 1. Generally, major minerals such as, Na, K, Ca, Mg, Cl, P, S are required more than 50 mg/day, trace minerals such as Fe, I, Zn, Se, Cu, Mn, Cr, Mo, Co, Ni which are needed less than 50 mg/day (Ismail et al. 2011). The analysis revealed that the consumption of this snack will provide major minerals such as Ca and trace minerals such as Fe, Zn, Cu, Mn, Ni for the consumers. It is said that the Recommended Dietary Allowance (RDA) values for Ca, Fe, Zn, Cu, Mn, Cr and Ni are 800–1200 mg/day, 10–18 mg/day, 15 mg/day, 1–3 mg/day, 1–5 mg/day, 0.02–0.2 mg/day and 0.13–0.4 mg/day respectively (Obiajunwa et al. 2002). The snack is free of heavy metals such as Pb and Hg. But this unroasted snack contains 4.37 ± 0.27 ppm of Arsenic. The quality criteria applied to edible seaweeds sold in France has reported that the Arsenic level in seaweeds that is consumed should be less than 3.0 ppm (Burtin 2003). Thus, in that point, the Arsenic level in the processed snack is higher than that of the specified limit. Previous research studies also states that the mineral content of water where seaweed has grown directly affect for the mineral composition of that seaweed variety (Marsham et al. 2007). Ulva fasciata samples for the product was obtained from the sea shore of Mirissa, Matara, Down South, Sri Lanka. Since there is a harbor close by, there is a high possibility of contaminations in U. fasciata samples. Hence, when utilizing seaweed in the food industry, the producers must consider the water quality parameters of the harvested area.

Table 1.

Elemental composition of processed snack with U. fasciata from Mirissa, Matara, Sri Lanka

Element	Elemental composition of snack (ppm)
K	ND
Ca	13,700 ± 707
Mn	121.0 ± 32.5
Fe	885.0 ± 91.9
Cu	35.95 ± 3.61
Zn	22.60 ± 1.56
Pb	ND
Bi	ND
Br	665.0 ± 55.2
Sr	153.5 ± 14.8
As	4.37 ± 0.27
Rb	7.09 ± 0.64
Ni	58.9 ± 1.41

Colour

According to the results, L* a* b* colour values for U. fasciata slurry are, 12.32 ± 0.20, − 8.14 ± 0.34 and 12.96 ± 0.49 respectively. L* a* b* colour values for U. fasciata snack are, 29.28 ± 1.14, − 6.16 ± 0.25, 12.52 ± 0.81 respectively. According to the statistical analysis L* and a* values are significantly different (P < 0.05). Thus, U. fasciata slurry is lighter than the snack. Drying process has led to a product darker in colour than the fresh slurry of U. fasciata. All a* values are negative by indicating high purity of green colour in U. fasciata slurry compared to U. fasciata snack. Researches have stated that Chlorophylls are directly related to magnesium. During drying, the magnesium molecules are changed to pyropheophytin and pheophytin. Therefore, at higher temperatures greenness is reduced. Visually, dark green colour of the leaves seemed as dull green–yellow due to degradation of chlorophyll (Ali et al. 2014). According to the statistical analysis of the results, yellowness of the U. fasciata slurry and U. fasciata snack are not significantly different (P > 0.05). Thus drying process has not affected the yellowish nature.

Conclusion

The snack has a high mineral, protein and a fiber content. The thickness, hardness, cohesiveness, springiness, gumminess and chewiness of the unroasted snack were, 0.30 ± 0.09 cm, 0.1 N, − 5.46, 14.87 mm, − 54.6 g and − 7.99 mJ respectively. The best preferred ginger concentration for the snack was 200 ppm. As the final outcome of the study, a crispy seaweed based snack from U. fasciata which is appealing to the taste of the South Asian region was successfully developed.