Changes in Maillard reaction of pidan white were monitored with A294, fluorescence intensity, and browning intensity during pickling in the absence and presence of Chinese black tea extract (Camellia sinensis) at levels of 2% and 5% together with 0.2% ZnCl2 or 0.2% CaCl2 up to 3 wk, followed by ageing for another 3 wk. Browning intensity and A294 of pidan white increased with increasing pickling/ageing, while fluorescence intensity decreased during ageing (p<0.05), irrespective of treatments. At wk 6, pidan white treated with 0.2% ZnCl2 and 0.2% CaCl2 showed slightly higher browning intensity, fluorescence intensity and A294 than those treated with divalents together with Chinese black tea (p<0.05). Free amino group and sugar contents showed continuous decrease during pickling and ageing irrespective of tea and cations used. However, pidan treated without Chinese black tea extract showed significantly lower free amino group and sugar during the ageing of 6 wk (p<0.05). Thus, Chinese black tea extract had an inhibitory effect on the Maillard reaction during ageing of pidan white.
Pidan and salted duck eggs are of nutritional rich alternative duck egg products which are predominantly consumed in China, Thailand, South Korea and other Chinese migrated countries. Both eggs are rich in proteins, lipids, unsaturated fatty acids and minerals. A Pidan whole egg contains 13.1% of protein, 10.7% of fat, 2.25% of carbohydrate and 2.3% of ash, whereas the salted duck egg contains 14% of protein, 16.6% of fat, 4.1% of carbohydrate and 7.5% of ash. The fresh duck egg contains a range of 9.30-11.80% of protein, 11.40-13.52% of fat, 1.50-1.74% of sugar and 1.10-1.17% of ash. Proteins, lipids, and ash contents are found to be greatly enhanced during the pickling and salting process of pidan and salted duck eggs. However, the alkaline induced aggregation of pidan leads to degradation and subsequent generation of free peptides and amino acids. Very few amino acids are found to be lost during the pickling and storage. However, no such losses of amino acids are reported in salted duck eggs during the salting process of 14 d. Phospholipids and cholesterol contents are lower in pidan oil and salted duck egg yolk oil. Thus, the pidan and salted duck eggs are nutritionally rich alternatives of duck egg products which will benefit the human health during consumption.
Impact of pulsed electric field (PEF) assisted process on preparation of custard apple leaf extract (CALE) using ethanol (70%, v/v) was studied. Different electric field strengths (2-6 kV/cm), pulse numbers (100-300 pulses) with specific energies (45-142 kJ/kg) for 2.5 to 5 min were implemented. Cell disintegration index was higher in CALE when PEF 6 kV/cm, 300 pulses, 142 kJ/kg for 5 min was applied. Extraction yield was higher (+5.2%) than the untreated counterpart (13.28%). Chlorophyll A and B contents were negligible in PEF pre-treated CALE. PEF improved radical scavenging activities assessed by DPPH, ABTS radical scavening activities and FRAP. The antibacterial properties of CALE against Staphylococcus aureus and Escherichia coli were highest. Purpureacin 2 and rutin were abundant in PEF pre-treated CALE. Therefore PEF was the potential aid in augmenting extraction yield and bioactivities of the extract from custard apple leaves.