How to use _sortBy in an array of objects that contains nested array of objects

I have a list of array of objects that contains a nested array of objects like so:

const mainList = [
{
    id:'001',
    category: 'A',
    content: [ 
        {
            title: 'Apples',
            language: 'en'
        },
        {
            title: '苹果',
            language: 'zh-cn'
        },
        {
            title: '苹果HK',
            language: 'zh-hk'
        },
    ],
},
{
    id:'002',
    category: 'B',
    content: [
        {
            title: 'Grapes',
            language: 'en'
        },
        {
            title: '葡萄',
            language: 'zh-cn'
        },
        {
            title: '葡萄HK',
            language: 'zh-hk'
        },
    ],
},
{
    id:'003',
    category: 'C',
    content: [
        {
            title: 'Bananas',
            language: 'en'
        },
        {
            title: '香蕉',
            language: 'zh-cn'
        },
        {
            title: '香蕉HK',
            language: 'zh-hk'
        },
    ]
}
]

I want to display this list using lodash _sortBy, by its title in alphabetical order like this:

Apples, Bananas, Grapes

My approach:

console.log(_sortBy(mainList.content.title))

But the result comes back with undefined at index 0

Thanks in advance!