The effect of maturation process on chemical and sensory properties of Palmaria palmata

The high demand for sustainable and healthy food is caused by the rapid growth of the world population. The ocean has an enormous potential to produce food for humans and feed for animals. However, this potential has not been fully exploited despite the high potential ocean food-producing. Macroalgae, both cultivated and wild harvested are popular in Asian countries, while it is mainly through wild harvesting for Western countries. Macroalgae as food for humans and feed for animals has not much been utilized in the West especially in Europe. This thesis is a part of the PROMAC project which has worked on three macroalgae species Alaria esculenta, Sacchina latissima and Palmaria palmata. The objective of this master thesis is to evaluate how the storage conditions with different moisture content in the P. palmata (Dulse) samples affect chemical and sensory characteristics. The effective storage conditions should not only maintain the soluble protein content but also improve the flavor of the seaweed. The red seaweed P. palmata harvested in France in November 2017 was the study target. The moisture content (MC) and water activity (aw) of air-dried samples were around 6% and 0.28 respectively. While in matured samples, MC was 20% with an aw approximately 0.62. For the total soluble protein content, the commonly used Lowry method was applied. According to the obtained data, the air-dried control sample D-126 showed the highest level of total soluble protein content with 30.33 mg/g DW. After 126 storage days, there was an increase by 8mg/g DW from 22.17 mg/g DW in D-0 sample to D-126 sample. The remaining samples in the same testing group did not show any changes in total soluble protein level after storage. However, the FD control group resulted in a significantly lower value with only around 11 mg/g DW. The total soluble protein contents in all matured samples were around 21 mg/g DW. The total soluble free amino acids (FAA) content of all samples was evaluated by HPLC. The total soluble FAA level decreased by 50% in both control groups. The freeze-drying step after storage did not affect the total soluble protein level since no difference was detected between D-126 and D-126 NFD samples. Only the total soluble protein level in the semi-hydrated samples stayed the same regarding different storage days. The FAA profile from HPLC results showed that glutamic acid was the most abundant, followed by alanine and aspartic acid. The content of glutamic acid and aspartic acid decreased after 126 days of storage in both FD and D control groups. However, the level of alanine declined during the maturation time only in the FD control group to half the value compared to this level the FD-0 sample. While the three semi-hydrated M-12, M-61 and M-126 samples showed the stable amount of these 3 FAA regardless of the storage days. From the sensory analysis, the control sample D-126 and the early matured samples M-12 had stronger marine taste including seaweed and fish skin aroma and dried-fish in flavor. These two samples also were more tough and crunchy in texture. Whereas, the marine taste faded, and the texture was softer in longer matured time sample. The two samples M-61 and M-126 had sweeter taste. M-61 had the highest score in hay aroma and the least score in a bitter taste. According to the outcome of the presented analysis, M-61 samples showed a stable amount of total soluble protein and FAA. Moreover, M-61 not only had a less marine and bitter taste with softer texture but also richer in sweet taste and flavor richness as umami taste. This is the most optimal sample among the 4 sensory testing samples. Although 20% in moisture content showed a stable amount of total soluble protein and free amino acids content, further studies are needed to find out the optimal moisture content and time of maturation to obtain higher value in protein and a richer flavor