Colour Preservation of Salted Gracilaria lemaneiformis by Hot Water Extraction of the Formed Brown Materials

The browning of Gracilaria lemaneiformis during salting decreases the sensory quality and commercial value of this alga. This study determined whether or not hot water treatment preserves the colour of salted G. lemaneiformis. During hot water treatment, brown materials were dissolved in hot water and separated from G. lemaneiformis, which resulted in the recovery of the natural colour of the alga. The optimised colour preservation conditions were 100°C extraction temperature and 20 min extraction time. Hot water treatment can potentially preserve the colour of G. Lemaneiformis.


Gracilaria
lemaneiformis of the family Gracilariaceae (Rhodophyta) is widely distributed in the marine environment; members of this family are principal sources of agar (Fan et al., 2012a).The commercial mariculture of G. lemaneiformis is currently a leading industry in China because of the high adaptability and rapid growth of this alga as well as its potential to improve the water environment and produce high agar concentration (Li et al., 2008).G. lemaneiformis exhibits anti-tumour (Fan et al., 2012a), immunomodulatory (Fan et al., 2012b) and antiinfluenza virus (Chen et al., 2010) activities.This alga is also a popular food resource in China because of its unique flavour and rich nutrition.
G. lemaneiformis contains 14.65% sugar, 21% protein, 0.87% lipids and relatively high levels of vitamin C, iodine, phosphorus and zinc (Wen et al., 2006).As a highly perishable commodity, G. lemaneiformis starts deteriorating immediately after harvesting.Thus, fresh G. lemaneiformis must be processed to extend its shelf life for off-season use.Salting is a common preservation method.However, G. lemaneiformis browning during salting and storage decreases the sensory quality and commercial value of the salted products.
We previously reported that the formed brown materials can be dissolved in hot water.Therefore, we determined whether or not hot water treatment preserves the colour of salted G. lemaneiformis and optimised the extraction conditions.

MATERIALS AND METHODS
Materials: Salted G. lemaneiformis was purchased from a local farmer market in Xinpu, China.
Treatments of the salted G. lemaneiformis: Salted G. lemaneiformis (10 g) was added to a beaker containing 100 mL of tap water.The beaker was maintained in a thermostatic water bath or a steriliser at 100°C for 20 min.The reaction mixture was filtered and the filtrates were subjected to colour evaluation.

Colour determination:
The colours of the extracts were measured using a CR-400 Minolta chromometer at room temperature.The colour of each extract was measured thrice using the CIE Lab L*(lightness), a* (redness-green) and b* (yellowness-blue) system.The changes in the colours of the extracts can be expressed as a single numerical value, ΔE, which defines the magnitude of the total colour difference as follows (Aguiló-Aguayo et al., 2009): where a o , b o and L o are the CIE-Lab values of tap water.

Statistical analysis:
All tests were performed in triplicate and data are reported as means ± SD.

ΔE
brown materials in salted G. lemaneiformis could be dissolved at temperatures above 100°C.Therefore, the optimal extraction temperature was 100°C.
Effect of hot water on the colour preservation of G. lemaneiformis: Under optimum extraction conditions, i.e., 20 min extraction time and 100°C extraction temperature, the colour of salted G. lemaneiformis returned from brown (Fig. 3A) to green (Fig. 3B), i.e., the original colour of fresh G. lemaneiformis.At the same time, the colour of the extracts turned from the original achromaticity to brown.This result indicated that the brown materials in the salted G. lemaneiformis could be dissolved in hot water at 100 °C.

CONCLUSION
The brown materials in salted G. lemaneiformis could be dissolved and extracted using hot water treatment.The efficiency of the extraction of the brown materials in salted G. lemaneiformis was affected by extraction time and temperature.Under optimum extraction conditions, salted G. lemaneiformis returned to its original green colour.Thus, hot water treatment may potentially preserve the colour of salted G. lemaneiformis.

Fig. 1 :
Fig. 1: Effect of time on the hot water extraction of brown materials in salted Gracilaria lemaneiformis