**1. Introduction**

Sausage is a popular meat product manufactured from different meat species such as pork, beef, chicken, fish, and buffalo [1–3]. This kind of meat product has important economic value for the meat-packing industry and is relished by consumers around the world for its delicious taste and high nutrition. In order to produce the sausages with high quality, nitrite is widely used as a preservative that can control foodborne pathogens [4]. Moreover, the additional function of the nitrites is to prevent lipid oxidation and rancidity, facilitate stabilization of the bright red color, and guarantee a typical "cured" flavor [5–7]. To fight against lipid oxidation, the nitrites could be associated with the binding of heme and prevent the release of the catalytic iron [8]. For keeping the bright red color of meat products, the nitrites can bind to myoglobin, forming the heat-stable NO-myoglobin. However, due to the reaction between nitrites and protein components in meat resulting in the carcinogen nitrosamine formation, the nitrites have been classified as potentially carcinogenic agents by the International Agency for Cancer Research of World Health Organizations (WHO) [9,10]. Consequently, it is important to obtain healthier meat products with a low content of residual nitrite without compromising the quality of the sausage.

Recently, researchers have focused on finding ways to decrease the additional content of nitrite in meat products, especially replacing it with natural resources such as vegetables, mushroom, and their extracts [11–14]. The reports showed that a part of plant essential

**Citation:** Wu, X.; Wang, P.; Xu, Q.; Jiang, B.; Li, L.; Ren, L.; Li, X.; Wang, L. Effects of *Pleurotus ostreatus* on Physicochemical Properties and Residual Nitrite of the Pork Sausage. *Coatings* **2022**, *12*, 484. https:// doi.org/10.3390/coatings12040484

Academic Editor: Maria Jose Fabra

Received: 25 February 2022 Accepted: 2 April 2022 Published: 4 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

oils exhibited strong antioxidative, antimicrobial, anticarcinogenic, and antimutagenic properties, which could be a compressive solution to substitute the nitrite [12]. For instance, Tang et al. (2021) reported that the combination of *Flos Sophorae* and chilli pepper can improve redness and reduce lipid oxidation of the meat product to replace nitrite in processed meat [15]. Vegetable powder extracted from radish and beetroot can substitute nitrite in sausage and increase the weight loss of sausages [16]. However, the studies on mushroom sausages have mainly focused on the nutritional components and sensory evaluation of the sausages and less concentrated on reducing the content of nitrite by adding edible mushrooms to sausage [17–19].

The mushroom is not only popular for its taste and flavor, but also for its high nutritional value and bioactive compounds. The addition of edible mushrooms to meat products can be used as a substitute for salt and phosphates in the formula of meat products and improve the quality of meat products, protein, dietary fiber, and ash content [20]. For example, the addition of shiitake mushrooms to sausage can improve the antioxidant and antibacterial properties of the product [21]. Replacing pork lean meat with *Lentinus edodes* can enhance total dietary fiber content, total phenol content, and the 2,2-diphenyl-1 picrylhydrazyl (DPPH) scavenging ability of sausage [22].

*Pleurotus ostreatus* (PO) is rich in amino acids (glutamic acid, aspartic acid, and arginine), polysaccharides (PSPO-1a, PSPO-4a, and branched β-glucans and α-glucans), vitamins (riboflavin and ascorbic acid), and dietary fiber with the function of antioxidant, antitumor, hypoglycemic, lipid-lowering, anti-inflammatory, sterilization, liver protection, improving immunity, and other significant effects [23–27]. Herein, a novel sausage incorporated with the *Pleurotus ostreatus* (PO) puree was developed to reduce the residual nitrite content in low-meat sausages during storage. Five recipes with the supplement proportion of 0 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.% PO were produced and their compositions, water activities, textures, colors, water holding capacities (WHC), amino acid compositions, and sensory evaluation were characterized. During storage at 4 ◦C, several characterizations including residual nitrite analysis, lipid oxidation analysis, and microbiological analysis were employed to characterize the quality and shelf-life of the products on days 0, 5, 10, 15, and 20.

### **2. Materials and Methods**

### *2.1. Materials*

The lean pork meat and back fat were purchased from the local market (WalMart Inc., Bentonville, Arkansas, USA) in China and stored at −20 ◦C. The fresh *Pleurotus ostreatus* (PO), salt, sugar, white pepper, cinnamon, and dry starch were also purchased from the local market (WalMart Inc., Bentonville, Arkansas, USA) in China. All other additives and chemical reagents shown in Table 1 were purchased from Sichuan Jinshan Pharmaceutical Co., Ltd. (Chengdu, China) and Beijing Beihua Co., Ltd., (Beijing, China).

**Table 1.** Formulations of *Pleurotus ostreatus* (PO) pork sausages.


### *2.2. Formulations and Processing of Sausage*

Table 1 shows the formulations of the PO pork sausages with different PO contents. The sausages with 0 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.% PO were named as the Control, PO10, PO20, PO30, and PO40, respectively. The content of PO supplement used to process the sausages was based on the total content of pork lean meat and pork back fat.

To process the sausages, the pork lean meat was first sliced into sections and pickled at 4 ± 1 ◦C for 24 h with salt, sugar, sodium tripolyphosphate, and sodium nitrite. Then, the pork back fat was cut into cubes with a side length of 1 cm. The PO was cleaned with water, cut into small pieces, and mashed with a chopping machine into the puree. According to the formulation of each group, the pickled pork lean meat, PO puree, white pepper, cinnamon, carrageenan, isolated soy protein, dry starch, *Monascus*, ice, and back fat were mixed homogeneously in a mixer (Busch, Marburg, Germany) for 140 s. After that, the mixture was filled into the artificial collagen casings with a diameter of 2.6 cm by a sausage filler (Guangdong Shunde Fangzhan Electric Industrial Co., Ltd., Foshan, China). The methods of cooking, cooling, and preserving sausages were the same as the method reported by Wang et al. (2013) [28]. Finally, the sausage was stored after vacuum packing (Shandong Xiaokang Machinery Co., Ltd., Weifang, China) at 4 ◦C, which was counted as day 0.
