As one of the most essential polyunsaturated fatty acids (PUFAs), omega-3 (n-3) PUFAs play an important role in the development of human beings’ nervous systems and protection against cardiovascular disease, as well as the prevention of breast and colorectal cancers [1
]. With consumer’s increasing awareness about health benefits of PUFAs [4
], a variety of functional foods fortified with PUFAs have been developed, among which n-3 PUFAs enriched egg is becoming more and more popular. The egg is not only an important source of nutrients for the human being [5
] but is also considered as an ideal delivery system for n-3 PUFAs, as its composition can be modified to more functions through the manipulation of laying hen diets [5
]. Hens fed with n-3 PUFAs enriched diets, such as fish oil, seaweed, and flaxseed can produce eggs enriched with n-3 PUFAs [3
] and provide a new way for the human being to enhance the intake of n-3 PUFAs in diets.
Like conventional eggs, n-3 PUFAs enriched eggs are also highly perishable, whose freshness and quality start to decline as soon as laid by hens [8
] and through the whole supply chain from poultry farm to consumers’ dining table. Egg quality is further influenced by both extrinsic (such as environmental conditions) and intrinsic factors (such as nutrients and water activity). The main environmental factors affecting these processes are the storage temperature and humidity [11
] as well as storage time [15
] during commercial circulation after laying until consumption.
Home storage is the last but not the least important stage in the eggs supply chain [16
]. Refrigeration is believed to be the most commonly used method to preserve internal egg quality [19
] at home, hence the eggs are recommended to be kept under refrigeration at home in the European Union (EU) countries [20
] and Egg regulations of United States Department of Agriculture (USDA) [21
] required the cooler should be capable of maintaining an ambient air temperature of 7.2 °C or lower and a relative humidity of 40 to 70 percent for a long time storage of eggs. However, there are no regulations or suggestions to tell consumers how to keep eggs at home in China yet. Data on the effects of storage conditions on n-3 PUFAs enriched eggs quality are very limited and even few studies have covered the time-temperature history of eggs after shopping until consumption during home storage.
As an advanced technology, wireless sensor network (WSN) is a combination of sensor technology, embedded networking, wireless communication technology and the distributed processing [22
]. It can sense and transmit the information of environments to the client-sides via the wireless network. WSN has many merits over a traditional data monitoring system [23
] for its higher accuracy and speed on data acquisition, wireless and real-time transmission, better flexibility and lower costs, and has been widely used in many application areas including medical field [24
], food safety [26
], environmental monitoring [29
], and etc. Therefore, WSN is considered as a good choice to monitor the changes of environment for home storage of eggs.
The objective of the present study is three-fold, (a) to quantify the effects of different home storage conditions (room temperatures vs. refrigeration) on shell eggs quality; (b) to compare the quality change between n-3 PUFAs enriched and conventional eggs; (c) to identify the optimum duration (days) to store shell eggs in a home refrigerator and under room temperature. The remainder of the paper is organized as follows: Section 2
describes the experimental design and the WSN based environment-monitoring scheme, Section 3
presents the temperature and humidity fluctuation monitored during the experiment and the quality changes of n-3 and conventional eggs during storage. The conclusions are provided in Section 4
2. Materials and Methods
Eggs for this research were collected from Shuangyin Poultry Farm located in Pinggu, Beijing, China and produced by Hy-line Brown (Hy-Line International, West Des Moines, IA, USA) laying hens of 30 weeks of age. Two groups of laying hens were fed with two kinds of different diets: one with n-3 PUFAs enriched diet for n-3 PUFAs enriched eggs (72% corn, 26% soybean, and 2% seaweed powder), and the other with standard diet for conventional eggs (74% corn and 26% soybean). Sample eggs were collected, packaged and delivered by SF Express (Beijing, China) immediately on the same day they were laid, arriving at the laboratory on the following day.
As soon as the eggs arrived at the lab, eggs were candled to take out defects (cracked, broken, and stained) and weighted. A total of 200 n-3 PUFAs enriched eggs and 200 conventional eggs were selected respectively for the experiment.
2.2. Experiment Design
Two scenarios, room temperature (scenario 1) and refrigeration (scenario 2) conditions were designed to simulate home egg storage in June 2017 in the Laboratory of Food Quality and Safety at China Agriculture University, (Beijing, China). Eggs in scenario 2 were put in a refrigerator (BCD-251WDPV, Haier, Qingdao, China) set to 4 °C for the duration of the study.
Both n-3 PUFAs enriched and conventional eggs were randomly divided into two groups (100 eggs per group) for two scenarios respectively. In each scenario, the eggs were numbered and put into egg trays. To evaluate the change of egg quality during storage, 5 conventional eggs and 5 n-3 PUFAs enriched eggs from each scenario were taken out separately and measured orderly at intervals of three days during the experiment period.
2.3. Monitoring Scheme
The WSN were utilized for real-time monitoring of temperature and humidity during eggs’ storage in two scenarios. The WSN architecture was composed of two sensor nodes, a network coordinator and the wireless network (Figure 1
The sensor node is an integration of a microcontroller, an antenna with a 433 RF module, storage and clock chips, temperature and humidity sensors and power supply (Figure 2
a). The microcontroller (STC12LE5A60S2, STCTM, Shanghai, China) were used to interconnect the slave modules and realize the functionality of sensor nodes by improving processing speed and the capacity of interference resistance. The antenna with a 433 RF module was designed to communicate with the coordinator, which performed low power consumption and high mobility performance. The clock chip can offer the time when data was collected, and the storage chip was used to save the sensor and time information. Six lithium batteries (LR6-4B/1.5 V, Nanfu, Nanping, China) were used to supply voltage for the sensors.
Temperature and humidity data were monitored by the digital sensors AM2302 (AOSONG, Guangzhou, China), whose data accuracy for temperature and humidity was 0.1 °C and 1% respectively. The working parameters of AM2302 are as follows: temperature ranges from −55 to +125 °C, relative humidity from 0% to 99%, operating voltage between 3.0 and 6.0 V.
The network coordinator was constructed of a wireless microcontroller, the General Packet Radio Service (GPRS) transmission module (WG 8010-485, Comway, Lewes, MD, USA), the crystal oscillator, and the antenna with an amplifier and power supply (Figure 2
b). The environmental data were transferred to the network coordinator for grouping and then sent to the client side by the GPRS module. The CC2530 module (TI, Dallas, TX, USA) was chosen as the wireless microcontroller to integrate the slave modules and optimize their performance.
2.4. Egg Quality Parameters
Haugh unit (HU), yolk index (YI) and albumin pH are commonly used parameters indicating egg quality [8
] and are adopted in this experiment to evaluate the freshness change of eggs during storage.
The whole egg weight was measured by a digital weighing scale (DL-X01, Donlim, Foshan, China) with precision of 0.01 g. After being weighed, the egg was broken onto a white flat plate. The HU value was calculated using the formula
], where H is the thick albumen height (mm) and W is the weight (g) of a whole egg. The thick albumen height was measured by averaging three measurements taken at different points of the thick albumen at a distance of 10 mm from the yolk by a sliding caliper (YB5002B, OK-TOOLS, Hangzhou, China). The yolk index is obtained by dividing the height by the diameter of the yolk [33
], and the yolk height and diameter were measured by the same sliding caliper. Albumin pH was measured by the pH meter (testo 206, lenzkirch, Fort Baden, Germany).
The experiment was ended when the HU decreased to 55 or YI down to 0.15 according to USDA’s egg regulation [21
] when eggs are inedible.
2.5. Statistical Analysis
One-way analysis of variance (ANOVA) and Least Significant Difference (LSD) were used to analyze significant difference among the eggs under two scenarios by IBM SPSS statistics 20 (IBM, Chicago, IL, USA, 2011). All statements of significance are based on p < 0.05 unless otherwise specified. The data regression, fitting and processing were performed by using MATLAB 2013b software (Math Works, Natick, MA, USA, 2013).