Introduction

One of the food products that can be developed from seaweed is a thin dried sheet product, or “nori”.Nori is produced by processing of the red seaweed Porphyra, and it is commonly consumed by the people of Japan, Korea, and China. Nori can be directly consumed as a snack or used as an edible wrapper (e.g., with sushi).^1-2 In Indonesia, nori products are mostly imported from other countries, as its consumption is still limited,especially among the middle and upper classes.

Due to increasing demand fornori, researchers are assessing the possibility of producing nori-like products using other seaweeds. For example, Loupatty³ explored the potential of Porphyra marcossi as a raw material for the production of a nori-like product.Other types of seaweed, such as the red seaweed Gelidium sp. and the green seaweed Ulva lactuca(U. lactuca), could also be used. This nori-like product made from the mixture of Gelidium sp. and U. lactuca seaweeds is a new product that we named “geluring”. Geluringcan be produced by modifying the commercial method of nori production.

Gelidium sp. and U. lactuca grow well in the coastal water of Indonesia, especially near coral reefs.^4-5 These seaweeds, which contain bioactive compounds such as sulfate polysaccharide, phenolics, flavonoids, and chlorophylls,^6-7 have the potential to be used as raw materials to produce healthy and/or functional foods. Ulva lactuca has high chlorophyll content (21.27 mg/g)⁶ and dietary fiber content.⁸ To date, this species has not been utilized optimally in Indonesia.

The goal of this study was to evaluate the chemical characteristics (proximate composition, dietary fiber, total phenolic, and flavonoid contents; and antioxidant activity) of geluring prepared from the mixture of Gelidium sp.and U. lactuca. Three types of geluring were studied [P1 (unseasoned), P2 (seasoned), and P3 (seasoned and roasted)], and results were compared with those of the raw materials.

Materials and Methods

Geluring Processing

Dry Gelidium sp. and U. lactuca were obtained from a local collector from Sayang Heulang Beach, Pameumpuk, Garut, West Java, Indonesia. The nori-like product was processed according to the method of Zakaria et al.,⁹ with modifications including soaking in vinegar and  heat treatment on the preparation of the pulp.

Dried seaweeds were washed and soaked with water (ratio1:2) for 24 hours for Gelidium sp. and 6 hours for U. lactuca. Samples then were soaked in 2% vinegar(ratio 1:1) for 30 minutes. The soaked sea weeds were washed with water, drained, cut into small pieces, and blended with water (ratio 1:1) using a commercial blender(Philips HR 2116). The pulp of U. lactuca was prepared by adding water (ratio 1:1) and cooking at 90–100^oC for 30 minutes. For Gelidium sp., the pulp was prepared by adding water (ratio1:9) and cooking at 90–100°C for 2 hours. The three geluring products prepared during the study were:

P1: Unseasoned geluring was produced bymixing Gelidiumsp.pulp and U. lactuca pulp (ratio 3:1 (256 g)) in a 12×38 cm mold and drying the mixture in an oven (Cascade Tex, USA)at 50^oC for 2 hours.

P2: Seasoned geluring was produced by the same process used to make P1, but seasoning made from 0.1% salt, 0.1% garlic powder, and 0.1 % pepper powder was added to the mixture.

P3: Seasoned and roasted geluring was produced by the same process used to make P2, but the produced dry sheet was smeared with coconut oil and roasted at 100^oC (Sanyo SK-8600 FM, Jepang)for 2 minutes.

The P1, P2 and P3 geluring sheets were vacuum sealed in plastic packaging and stored at 4^oC in prior to analysis for not more than 3months.

Table 1: Proximate Composition of Geluring Products (P1, P2, P3) and Raw Materials

Values are expressed as mean±SD (n=3); different letters within columns indicate significant differences (p<0.05).

Table 2: Dietary Fiber, Total Phenolic Content, Flavonoid Content, and DPPH Antioxidant Activity of Geluring Products (P1, P2, P3) and Raw Materials

Values are expressed as mean±SD (n=3); different letters within columns indicatesignificant differences (p<0.05).

Proximate Composition

The proximate composition (moisture, protein, fat, ash, and carbohydrate) of geluring products and raw materials was determined according to AOAC¹⁰ methods. Carbohydrate analysis was conducted by different.

Dietary Fiber Content

Dietary fiber content was measured following the AOAC¹⁰ method.

Total Phenolic Content

Total phenolic content was measured using Folin-Ciocateu reagent(Sigma) with gallic acid as the standard(Sigma) based on the method described by Hodzic.¹¹ Solution absorbance was measured using a UV spectrophoto meter(Shimadzu UV-1800, USA)at 725 nm wavelength.

Flavonoid Content

Flavonoid content was measured using the aluminum chloride colorimetric method, with absorbance measured using a spectrophotometer¹² (Shimadzu UV-1800, USA).Quercet in (Sigma)was used as the standard.

Antioxidant Activity Measured by the 1,1-Diphenyl-2-Picryl-Hydrazyl (DPPH) Assay

Analysis of antioxidant activity was conducted using the DPPH method.¹³ Extraction of geluring products was performed by macerating the geluring product for 24 hours using water solvent at a concentration of 20 mg/ml. For analysis, 2 ml of each sample extract were reacted with 2 ml of 0.1 mM DPPH reagent(Sigma) and then placed in a dark room for 10 minutes. The solution absorbance was measured using a UV spectrophoto meter (Shimadzu UV-1800, USA)at 517nm wavelength.

Statistical Analysis

The design of the experiment was completely randomized. Analysis of variance followed by Duncan’s multiple range test were used to compare proximate composition, fiber content, total phenolic content, total flavonoid content,and antioxidant DPPH activity data among the treatments. P<0.05% was considered to be statistically significant.

Results and Discussion

Proximate Composition

Table 1 shows the moisture, protein, fat, ash, and carbohydrate content of the geluring products.The moisture, protein,and fat content did not differ significantly (P>0.05) between P1 and P2, but they did differ significantly (P<0.05) from P3. Theash and carbohydrate content of P2 and P3 did not differ significantly (P>0.05), but they did differ significantly(P<0.05) from P1. In general, proximate composition of geluring products was significantly different (P<0.05) from that of its raw materials. P3 geluring was high in fat content due to the addition of coconut oil prior to the roasting process. The fat content of coconut oil according is 85-95%.¹⁴

Geluring produced in this study had higher moisture, ash, and carbohydrate contents but lower protein and fat contents compared to commercial nori made from Porphyra seaweed.¹⁵ The difference in proximate composition between geluring products and commercial nori likely is due to the use of different seaweed types. Taboada et al.,¹⁶ and Polat and Ozogul¹⁷ reported that the proximate content of seaweed is affected by the type, harvest age, harvest period, post-harvest handling, and conditions of the sea environment.

Dietary fiber content

The fiber content of geluring products ranged from 29.19 to 29.82% (Table 2). No significant difference (P>0.05) in fiber content was detected among the geluring products, but they did differ significantly (P<0.05) from the raw materials. Dietary fiber content of geluring was higher than that of the raw material Gelidium sp., and the addition of U. lactucapulp during geluring preparation also successfully increased the dietary fiber content of the geluring product. Ulva lactuca is a green seaweed that is rich in dietary fiber.¹⁸ The dietary fiber content of U. lactuca used in this study was 50.21%, which was lower than the content (53–54.9%)reported by Yaich et al.,⁸ but higher than the content (28.4%) reported by Rasyid.¹⁹ Gelidium sp. in this study had dietary fiber content of about 20.12%, which was lower than the dietary fiber content of Gelidium pusillum (24.74%).⁷ The process of making geluring including soaking with acid, blending of seaweed, pulping and drying of the sheet may influence the fiber functionality of the geluring product compared to  that of the raw material. Treatment with acid was reported to improve the swelling properties of dietary fiber,²⁰ mechanical treatments such as stirring reportedly caused changes in the chemical structure of the fibers that can free hydroxyl groups in the fiber molecules making them readily bind to water.²¹ Likewise, heat processing is reported to alter the ratio of soluble and insoluble fiber and fiber surfaces.²²

Geluring in this study had a higher dietary fiber content than commercial nori, which  is about 23.1%.¹⁶ This difference is due to the difference in the dietary fiber content of the raw material.Dietary fiber content of Porphyra sp. is about 48%.²³ Although the dietary fiber content of the geluring products in this study was higher than that of commercial nori, the values were lower than that of the nori-like product prepared from the mixture of U. lactuca and Euchema cottoni (36.76%).⁹

Total Phenoliccontent

Total phenolic content of the geluring products ranged from 0.93 to 1.38 mg GAE/g, and values differed significantly (P<0.01) among allgeluring products and the raw materials(Table 2). P2 had higher total phenolic content compared to P1 and P3. The high total phenolic content of P2 was due to the addition of 0.1% garlic and 0.1% pepper. Kamath et al.,²⁴ and Lachowicz et al.,²⁵ reported that the total phenolic content of garlic is 0.065 mg and that of pepper is 1.76 mg GAE/g. Although P3 also contained pepper and garlic, the product was roasted at 100 °C, which could have destroyed some of the phenol substances. Amorim et al.,²⁶ reported that the heating process at high temperatures, such us roasting process could lower the phenolic content in seaweed.

The total phenolic contents of the geluring samples in this study were lower than those of the raw materials. Total phenolic contents of Gelidium sp. and U. lactuca were 6.33 mg and 5.91mg GAE/g, respectively, which is lower that the value for Porphyra (18.2 mg GAE/g), which is the raw material for commercial nori.²⁷ The geluring processing procedure includes cooking and drying, which could reduce the phenolic content. Xu and Chang²⁸ reported a 40–50% loss in the total phenolic content of legumes due to the boiling process. Cox et al.,²⁹ found that Himanthalia elongata seaweed steamed for 45 min lost around 32.06% of its total phenolic content. Watchtel-Galor et al.,³⁰ reported that steaming and microwaving caused loss in total phenolic content of broccoli, choysum, and cabbage. The thermal process can change the phenolic structure of phenol substances, causing the content to lessen.^31-33 The thermal process can also denature enzymes that are important for breakdown of nutrients and phytochemicals.³³

Flavonoid Content

Flavonoids are phenolic compounds that are found commonly in seaweeds.^34-35 Flavonoid content of the geluring products in this study ranged from 0.81 to 1.11 mg QE/g (Table 2). Significant differences (P<0.05) in the flavonoid content were detected among all geluring samples and raw materials. The flavonoid content of P2 was significantly higher than those of P1 and P3. The presence of garlic and pepper in P2 likely increased the flavonoid content. Priecina and Karlina³⁶ reported that the flavonoid content of garlic is 8.9 mg QE/g.

The flavonoid content of nori products is affected by the flavonoid content of the seaweed raw material. The flavonoid contents in the geluring samples were lower than those of the raw materials. The processing procedure used affects the content, activity, and bioavailability of bioactive compounds such as flavonoids.^28-30 Gupta et al.,³⁷ reported that the flavonoid content of H. elongata decreased to 30% due to drying at 25^oC but increased to 49% at 40^oC. Cox et al.,²⁹ found that boiling of H. elongata significantly reduced the flavonoid content within a range of 88.86 to 90.18%.

Antioxidant Activity

The antioxidant activity of the different geluring samples and raw materials all differed significantly from each other (Table 2). P2 had significantly higher antioxidant activity than P1 and P3. The addition of 0.1% garlic and 0.1% pepper likely accounts for the higher antioxidant activity in P2. Garlic and pepper contain bioactive components such as phenolics, which have antioxidant activity.^38-40 The lower antioxidant activity of P3 compared to P2 likely was caused by roasting of P3,which would destroy bioactive components in garlic and pepper.Antioxidant stability also is affected by temperature.⁴¹ Exposure to roasting temperature causes antioxidant compounds to become less stable due to chemical and physical degradation.^42-44

The antioxidant activities of P1 and P2 were higher than those of commercial nori, which is about 51%.¹⁵ The antioxidant activities of all geluring products were lower than those of the raw materials (Table 2). The cooking and drying process could have decreased the antioxidant activity. Hwang and Do Thi⁴⁴ and Susanto et al.,⁴⁵ reported that processing of seaweed by drying, steaming, and boiling can reduce antioxidant activity.Although high temperature  is used in the process of making gelurings, the product still has the antioxidant activity  to inhibit DPPH radical compound. These results are similar to those reported by Pina et al.,⁴⁶ that boiled and evaporated seaweed still has a high activity in inhibiting DPPH radical compound.

Conclusions

Geluring products made from the mixture of Gelidium sp. and U. lactuca had high carbohydrate and dietary fiber content and low fat content,contained bioactive components such as phenols and flavonoids, and exhibited antioxidant activity. These results show that geluring has potential for use as a functional food. However, further research is necessary to determine the benefits of geluring products and to identify biological functions of its components.

Acknowledgements

The authors would like to thank the Ministry of Research, Technology, and Higher Education of the Republic of Indonesia for providing financial support for this research.

References

1. McHugh D. J. A Guide to The Seaweed Industry. Food and Agriculture Organization of the United Nations, Rome. 2003.
2. Kuda T., Tsunekawa M., Hishi T., Araki Y. Antioxidant properties of dried ‘kayamo-nori’, a brown alga Scytosiphon lomentaria (Scytosiphonales, Phaeophyceae).Food Chemistry. 2005;89(4):617–622.
   CrossRef
3. Loupatty. Nori nutrient analysis from seaweed of Porphyra marcossi in Maluku ocean. Eksakta. 2014;14(2):34–48.
   CrossRef
4. Dewi R. Potency of seaweed resources. Journal Harpodon Borneo. 2012;5(2):125–129.
5. Rasyid A. Evaluation of nutritional composition of the dried seaweed Ulva lactuca from Pameungpeuk water, Indonesia. Tropical Life Sciences Research. 2017;28(2):119–125.
   CrossRef
6. El-Baky H. A., El Baz., F. K., El-Baroty., G. S. Evaluation of marine alga Ulva lactuca as a source of natural preservative ingredient. American-Eurasian. Electronic Journal of Environmental, Agricultural and Food Chemistry. 2008;7(11): 3353–3367.
7. Siddique M. A. M., Khan M. S. K., Bhuiyan M. K. A. Nutritional composition and amino acid profile of a sub-tropical red seaweed Gelidium pusillum collected from St. Martin’s Island, Bangladesh.International Food Research Journal. 2013;20(5):2287–2292.
8. Yaich H., Garna H., Bchir B., Besbes S., Paquot M., Richel A., Blecke  C., Attia H. Chemical composition and functional properties of dietary fibre extracted by Englyst and Prosky methods from the alga Ulva lactuca collected in Tunisia.Algal Research. 2015;9:65–73.
   CrossRef
9. Zakaria F. R., Priosoeryanto B. P., Erniati., Sajida. Characteristic of the nori from mixed Ulva lactuca and Eucheuma cottoni seaweeds. Journal of Postharvest, Fisheries and Marine Biotechnology. 2017;12(1):23–30.
10. Official Methods of Analysis AOAC International. The Association of Official Analytical Chemist, Arlington, VA. 2005.
11. Hodzic, Z., Pasalic, H., Memisevic, A., Srabovic, M., Saletovic, M., Poljakovic, M. The influence of total phenols content on antioxidant capacity in the whole grain extracts.European Journal of Scientific Research. 2009;28(3):471–477.
12. Chang C. C., Yang M. H., Wen H. M., Chern J. C. 2002. Estimation of total flavonoid content in propolis by two complementary colorimetric methods.Journal of Food and Drug Analysis. 2002;10(3):178–182.
13. Vijayabaskar P., Shiyamala V. Antioxidant properties of seaweed polyphenol from Turbinaria ornata (Turner) Agardh, 1848.Asian Pacific Journal of Tropical Biomedicine. 2012;2(1):S90–S98.
14. Soeka Y. S., Sulistyo J., Naiola E. Biochemical analysis of extracting fermented coconut oil. Biodiversita. 2008;9(2):91–95.
    CrossRef
15. [MEXT]. Ministry of Education, Culture, Sports, Science and Technology of Japan. Standard Tables of Food Composition in Japan . 7^rd.Tokyo, Japan. 2015.
16. Taboada M. C., Millán R., Miguez M. I. Nutritional value of the marine algae wakame (Undaria pinnatifida) and nori (Porphyra purpurea) as food supplements.Journal of Applied Phycology. 2012;25(5):1271–1276.
    CrossRef
17. Polat S., Ozogul Y. Seasonal proximate andfatty acid variationsof some seaweedsfrom the northeasternMediterranean coast. Oceanologia. 2013;55(2):375–391.
    CrossRef
18. Ortiz J., Romero N., Robert P., Araya J., Lopez-Hernandez J., Bozzo C., Navarrete E., Osorio A., Rios A. Dietary fiber, amino acid, fatty acid and tocopherol contents of the edible seaweeds Ulva lactuta and Durvillaea antarctica. Food Chemistry. 2006;99:98–104.
    CrossRef
19. Rasyid A. Evaluation of nutritional composition of the dried seaweed Ulva lactuca from Pameungpeuk waters, Indonesia.Tropical life sciences research. 2017;28(2):119-124.
    CrossRef
20. Bertin C., Rouau X., Thibault J. F. Structure and properties of sugar beet fibres. Journal of the Science of Food and Agriculture. 1988;44:15–29.
    CrossRef
21. Sangnark A., Noomhorm A. 2004. Chemical, physical and baking properties of dietary fiber prepared from rice straw. Food Research International. 2004;37:66–74.
    CrossRef
22. Elleuch M., Bedigian D., Roiseux O., Besbes S., Blecker C., Attia H. Dietary fibre and fibre-rich by-products of food processing: Characterisation, technological functionality and commercial applications: A review. Food chemistry. 2011;124(2):411-421.
    CrossRef
23. Cian R. E., Fajardo M. A., Alaiz M., Vioque J., González R. J., Drago S. R. Chemical composition, nutritional and antioxidant properties of the red edible seaweed Porphyra columbina.International Journal Of Food Sciences and Nutrition. 2014;65(3):299-305.
    CrossRef
24. Kamath S. D., Arunkumar D., Avinash N. G., Samshuddin S. Determination of total phenolic content and total antioxidant activity in locally consumed food stuffs in Moodbidri, Karnataka, India.Advances in Applied Science Research. 2015;6(6):99–102.
25. Lachowicz S., Kolniak‐Ostek J., Oszmiański J., Wiśniewski R. Comparison of phenolic content and antioxidant capacity of bear garlic (Allium ursinum) in different maturity stages.Journal of Food Processing and Preservation. 2017;41(1):1–10.
    CrossRef
26. Amorim K., Lage-Yusty M. A., Lopez-Hernndez J. 2012. Changes in bioactive compounds content and antioxidant activity of seaweed after cooking processing.CyTA-Journal of Food. 2012;10(4):321-324.
    CrossRef
27. Machu L., Misurcova L., Vavra Ambrozova J., Orsavova J., Mlcek J., Sochor J., Jurikova T., 2015. Phenolic content and antioxidant capacity in algal food products.Molecules. 2015;20(1):1118–1133.
    CrossRef
28. Xu B., Chang S. K. Effect of soaking, boiling and steaming on total phenolic content and antioxidant activities of cool season food legumes. Food Chemistry. 2008;110:1–13.
    CrossRef
29. Cox S., Abu-Ghannam N., Gupta S. Effect of processing conditions on phytochemical constituents of edible irish seaweed Himanthalia elongate. Journal of Food Processing and Preservation. 2011;36(4):348–363.
    CrossRef
30. Watchtel-Galor S., Wong K.W., Benzie I. F. F. The effect of cooking on Brassica Food Chemistry. 2008;110:706–710.
31. Jimenez‐Escrig A., Jimenez‐Jimenez I., Pulido R., Saura‐Calixto F. Antioxidant activity of fresh and processed edible seaweeds. Journal of the Science of Food and Agriculture. 2001;81:530–534.
    CrossRef
32. Capecka E., Mareczek A., Leja M. Antioxidant activity of fresh and dry herbs of some Lamiaciae Food Chemistry. 2005;93:223–226.
    CrossRef
33. Rungapamestry V., Duncan A. J., Fuller Z., Ratcliffe B. Effect of cooking Brassica vegetables on the subsequent hydrolysis and metabolic fate of glucosinolates.Proceedings of the Nutrition Society. 2007;66:69–81.
    CrossRef
34. Keyrouz R., Abasq M. L., Le Bourvellec C., Blanc N., Audibert L., ArGall E., Hauchard D. Total phenolic contents, radical scavenging and cyclicvoltammetryof seaweeds from Brittany. Food Chemistry. 2011;126:831–836.
    CrossRef
35. Farvin K. S., Jacobsen C. Phenolic compounds and antioxidant activities of selected species of seaweedsfrom Danish coast. Food Chemistry. 2013;138:1670–1681.
    CrossRef
36. Priecina L., Karlina D. Total polyphenol, flavonoid content and antiradical activity of celery, dill, parsley, onion and garlic dried in conventive and microwave-vacuum dryers. In: Proceeding 2^nd International Conference on Nutrition and Food Sciences IPCBEE. IACSIT Press. Singapore. 2013;53:107–112.
37. Gupta S., Cox S., Abu-Ghannam N. Effect of different drying temperatures on the moisture and phytochemical constituents of edible Irish brown seaweed. LWT-Food Science and Technology. 2011;44(5):1266–1272.
    CrossRef
38. Narendhirakannan R. T., Rajeswari K. In vitro antioxidant properties of three varieties of Allium sativum extracts.Journal of Chemistry.  2010;7(S1):S573-S579.
39. Martins N., Petropoulos S., Ferreira I. C. Chemical composition and bioactive compounds of garlic (Allium sativum) as affected by pre-and post-harvest conditions: A review. Food chemistry. 2016;211:41-50.
    CrossRef
40. Srinivasan K. Black pepper (Piper nigrum) and its bioactive compound, piperine. InMolecular targets and therapeutic uses of spices: Modern uses for ancient medicine. 2009;3:25-64.
    CrossRef
41. Plaitho Y., Rattanasena P., Chaikham P., Prangthip P. Biochemical and antioxidative properties of unprocessed and sterilized white and black sesame by-product from Northern Thailand.Current Research in Nutrition and Food Science Journal; 5(3): 196-205:
42. Lim Y.Y., Murtijaya J. Antioxidant properties of Phyllanthus amarus extracts as affected by different drying methods.LWT-Food Science and Technology. 2007;40:1664–1669.
    CrossRef
43. Sugiyono, Muchtadi T. R. Principles of process and food technology. Alfabeta, Bogor. Indonesia. 2013.
44. Hwang E. S., Do Thi N. D. Effects of extraction and processing methods on antioxidant compound contents and radical scavenging activities of laver (Porphyra tenera). Preventive Nutrition and Food Science. 2014;19(1):40–48.
    CrossRef
    
45. Susanto E., Fahmi A. S., Agustini T.W., Rosyadi S., Wardani A. D. Effects of different heat processing on fucoxanthin, antioxidant activity and colour of Indonesian brown seaweeds. IOP Conf. Series: Earth and Environmental Science. 2017 55;1–10:46.  Pina A. L., Costa A. R., Lage-Yusty M. A., Lopez-Hernandez J. 2014. An evaluation of edible red seaweed (Chondrus crispus) components and their modification during the cooking process. LWT-Food Science and Technology.2014;56(1):175-180.