Shanghai Baosheng Electronic Nose Helps Professor Yang Zhenquan's Team from Yangzhou University Publish Articles on the Effects of Different Drying Processes on Jincheng Peel

1. Research background

In recent years, citrus fruits have become increasingly popular worldwide for their delicious flavor and high nutritional value. Sweet oranges are usually sold fresh and are widely used in the food industry to make citrus foods, producing a large amount of by-products, especially the skin, which accounts for about 50-55% of the total weight of the fruit. Orange peel, as an agricultural waste, is widely discarded without realizing its potential nutritional value and bioactive components, resulting in serious environmental pollution and resource waste.

In many Asian countries, citrus peels (CFPs) have been traditionally used as health food and medicine for thousands of years. In pharmacology, CFPs are considered a rich source of various bioactive compounds, and in some cases, even a single source, including ascorbic acid, carotenoids, phenolic acids, flavonoids, sinomenine, limonene, etc. These compounds have excellent health promoting effects both in vitro and in vivo. Therefore, the concept of turning "waste" into "gold" and the various bioactive properties of CFPs have promoted the research on waste value-added components in many foods, cosmetics, pharmaceuticals, and health foods. However, CFPs contain high levels of moisture and are highly susceptible to decay due to fungal/insect contamination and mold growth, which is a major obstacle to their effective utilization.

Professor Yang Zhenquan's team from Yangzhou University published an article titled "Comparison of different drying technologies for brocade orange (Citrus sinensis) peels: Changes in color, physicochemical profile, volatile, and biological availability and activity of bioactive compounds" in the journal Food Chemistry (IF=8.8) (DOI: 10.1016/j.foodchem. 2023, 136539). The article mainly explores the physical properties, phytochemical characteristics, bioavailability, and antioxidant activity of the widely used Jin orange peel in orange juice production using different drying methods (freeze-drying, heat pump drying, microwave drying, far-infrared drying). The impact.

The instrument used to evaluate the similarity of aroma characteristics between samples in the article is our Shanghai Baosheng electronic nose. So, what is the specific operation method?

2. Experimental Methods

2.1 Sample Preparation

When commercially mature, randomly hand pick Jin oranges without physical injury or infection. The fruits were immediately transported to the laboratory, with uniform size and color, washed with tap water, and then air dried at 25 ° C. Afterwards, without damaging the segmented film, use a manual peeler to peel off the orange peel (BOPs), cut it into small pieces, mix thoroughly, randomly group them, and then perform drying operations.

According to the Pharmacopoeia of the People's Republic of China and the Chinese standard DB4407/t70 (2021), the production of CRP must be carried out at relatively low temperatures (≤ 45 ℃), and the moisture content of the final product must be less than 0.13 kg/kg dry weight (DW).

(a) Pre freeze at -80 ℃ for 4 hours, then freeze dry in a freeze dryer below -60 ℃ with a vacuum degree of<10 mbar for approximately 48 hours; (b) BOPs are dried in a heat pump dryer at a temperature of (43 ± 2) ℃, a relative humidity of 90%, an air flow rate of 1200 m3/h, and dried for 16 hours. Before each experiment, the dryer runs for 20 minutes to reach the desired temperature; (c) Place BOPs in a commercial microwave oven and dry for 35 minutes every 1 minute at 350 W; (d) Use an infrared dryer to dry at (43 ± 2) ℃ for 20 hours. Similarly, run the drying system idle for 20 minutes to reach the temperature before drying treatment.

2.2 Electronic Nose Analysis

The similarity of aroma characteristics between samples was estimated using an electronic nose (cNose, Shanghai Baosheng), which was coupled with ten gas sensors programmed for different types of aroma substances.

Fill 1.0 g of dry powder into a 20 mL headspace vial and incubate at 50 ° C for 30 minutes before measuring. Dry air is used as the carrier gas, with a flow rate of 400 mL/min, a cleaning time of 120 s, and a testing time of 90 s. Before each sample measurement, the electronic nose sensor is air rotated once to purify it. Finally, linear discriminant analysis (LDA) was performed on the data using the E-nose software system.

3. Experimental results

3.1 Analysis of Electronic Nose Results

The image shows the similarity of aroma spectra of volatile compounds from dried tangerine peel

Freeze drying (FD), heat pump drying (HPD), microwave drying (MD), and far-infrared drying (FID)

The electronic nose system can detect and analyze subtle changes in taste and aroma of different samples in real time and objectively, mimicking the human sense of smell. In response to the shortcomings of qualitative and semi quantitative analysis of aroma components in BOPs, electronic nose analysis is further utilized to characterize their overall volatile changes from another perspective. A stronger response to sample aromatic compounds was observed in sensors 3 and 8, indicating that BOPs may contain abundant ammonia aromatic components, inorganic sulfides, alcohols, and aldehydes. As mentioned above, the most volatile substances present simultaneously in all samples are limonene with citrus, aromatic, and fruit flavors, β - laurene with aromatic, resin, soap, and spicy flavors, and decanal with aldehyde, fat, floral, green, fat soap, citrus, and wax flavors, accounting for 67.80-89.15%, 2.31-5.58%, and 0.80-3.79% of the total volatile substances, respectively. Although these substances are considered key and influential metabolites, the lack of significant differences in response between sensors 3 and 8 may be closely related to the low odor threshold, which is only 10, 13, and 2 ppb, far exceeding the detection limit of gas sensors. On the other hand, the significant differences observed in sensors 1, 4, 5, 6, and 7 may largely depend on the distribution and concentration of volatiles. To be precise, linalool has a lower odor threshold at 6 ppb, with flavors of large spice, citrus, floral, and terpenes, while nonanal can be perceived in the flavors of aldehyde, citrus, fat, floral, green grass, slightly spicy, soap, oil, and wax at 1 ppb

Based on our data, the most striking result is that freeze-drying can largely maintain physical color and plant chemical characteristics, but its drying speed is slow and energy costs are high. It is estimated that the cost of freeze-drying is 4-8 times higher than that of convection drying, which limits the industrial scale applicability of freeze-drying. Therefore, freeze-drying is limited to high-value products such as instant coffee and edible and medicinal species. On the other hand, BOPs dried by heat pumps, especially microwave drying, have relatively attractive colors, high content of pigments, bioactive compounds and volatiles, as well as bioavailability and activity.